Insect and mollusk pests
WHAT IS THE HUGE GRUB THAT IS EATING BANANA ROOTS? Mat Huber sent us a large beetle in a bottle of alcohol. The beetle, larger and longer than your thumb, is causing serious damage to bananas in his part of Haiti. Dr. Frank Martin identified it as Cosmopolites sordidus, considered to be the number two problem of banana in the Caribbean, second only to Cigateca disease. It usually occurs in coastal locations; in the interior it usually does not limit banana production. (However, Mat is well inland and it is serious.)
Symptoms are a listless appearance of the plant and spindly leaves. About the only thing that can be done is when digging pups, clean them with a machete so carefully that you will notice damage if the beetle is present on the pup. Use only borer-free pups on clean land. The beetle is large but not very mobile, so infestation of the new planting might not occur if sufficiently distant from infested bananas. His reference book recommends treating pups with a systemic insecticide. Their recommendation, however, is an organophosphate now outlawed in this country because it could kill people!
BLISTER BEETLE CONTROL. Sina Luchen with the Ministry of Agriculture in Zambia sent suggestions on controlling blister beetles (drawing by Rose Elwell). "Recently we had an unusually high infestation of blister beetles (Mylabris sp.) in okra. This can be a devastating pest to a number of crops including beans, cowpeas, cucurbits, and maize by eating flowers, pollen and tender pods. One recommended method of control is hand picking. This must be done with care because the beetles secrete a liquid that causes blisters when it falls on human skin. Intensive sprayings with a number of recommended insecticides could not help much. ...I came across an agricultural bulletin from Lesotho in which it was reported that farmers there were controlling the beetle by use of blue containers filled with soapy water. This insect is irresistibly attracted to the color blue, flies into the container and drowns.
"We tried the technique. We bought 4 blue containers, filled them with detergent and placed them among the experimental plots which covered an area of 180 square meters. On the first day in an 8 hour period, 1200 beetles had drowned. It is recommended to cover the outside of the containers to avoid beetles hitting on the sides. Over a number of days, the infestation of the pest became drastically reduced. ...If the drowned insects are scooped out daily, the detergent can be reused for a number of days without having to change the liquid."
IDEAS FOR CONTROLLING CHICKPEA POD BORER. (From Int'l Agricultural Development, Jan/Feb 1994.) Chickpea leaves and pods exude extremely acidic (pH 2) droplets which repel most pests from attacking the plant. But recently the pod borer, which eats the contents of the pods, has become tolerant to the acid and has devastated crops in Asia. Pod borers have become resistant to many insecticides, and biological control is difficult because beneficial insects do not tolerate the acidic conditions.
Scientists at ICRISAT are breeding low-acid chickpeas and recommend wider planting which gives birds (like cattle egrets) paths to walk through the field to eat the caterpillars. Another creative way to control the pest is to intercrop the chickpeas with coriander, a commercial spice crop. Coriander has an umbel flower (like carrots or Queen Anne's Lace) which serves as a "platform" for predator insects to enjoy nectar and sun and an acid-free home from which they can attack the pod borer. Research showed that using these techniques enables Indian farmers to quadruple their chickpea yields.
TRENCH TRAPS CONTROL COLORADO POTATO BEETLE. Researchers at AgCanada and Cornell University have developed a technique to control the Colorado potato beetle, a major pest not only of potato but also of tomato and eggplant. The beetle is native to Mexico, where it actually feeds on two wild Solanaceous weedy relatives rather than the domesticated potato. It has spread throughout the United States (except California), from western Europe through the Mediterranean region all the way to China. Entomologist Prof. Ward Tingey of Cornell said that the beetle will likely reach North Korea by the year 2000. It is primarily a temperate pest, and does not exist as a crop pest south of Mexico or in the Andes, where potatoes are native. If this beetle is not a problem in your area, the technique may still be helpful with other beetles.
The Colorado potato beetle has become resistant to many pesticides. An innovative technique developed by AgCanada and researched by Cornell is the use of "trench traps" to catch the beetles as they walk out of fields in search of new food sources or places to overwinter.
This technique, like most successful pest control programs, relies on a knowledge of the insect's biological cycle. Farmers often rotate their potato crops to adjoining plots of land in an effort to control the beetle's damage to their plants. The effectiveness of this practice is increased by digging deep (minimum 30 cm/12 in, and up to 91 cm/3 feet) trenches around their fields and lining them with 1.5 mil black plastic mulch.
Potato beetles emerge from their winter hibernation in the soil in the previous year's field and disperse to the new field by walking up to 45 m (150 ft) from their hibernation site. They do not generally fly to find new food sources, as many other pests do. In an effort to reach the new potato field, the beetles fall into the plastic-lined trench, and, unable to crawl out, starve to death within 10-14 days.
The design of the trench is important to the success of this control method. It must have at least a 65 angle. The plastic lining is also key in the control: the beetles are able to climb out of the trenches if the plastic is clean (as when new, or just after a rain) due to their fine leg hairs, but they cannot crawl out when the plastic is coated with fine dust particles. Prof. Tingey recommends that growers place their trenches next to roads or well-used pathways so that they are redusted after a rain. Drainage of the trench is effected by perforating the trench bottom every 3m/10 feet. Though some insects may escape the trenches through these perforations, in test areas they have often been killed by a fungus, Beauveria bassiana, which thrives in the dark, moist areas below the trench. Farmers find masses of white webbed fungus on dead beetles when they peel back the plastic.
The technique can be used at both ends of the season: at the beginning, to trap insects as they attempt to enter a field, and at the end, as they leave the field to overwinter after the potato foliage is killed before the potato harvest. One main disadvantage is that the plastic does not usually last more than one year and needs to be replaced as new areas are dug.
The technique is not presently being used for control of other pests, although presumably it could be used for other beetles which disperse primarily through walking or crawling rather than flying. In Controlling Crop Pests and Diseases, Rosalyn Rappaport writes that army worms and cutworms, which migrate into crops by crawling, can be trapped and killed in ditches dug around plants. She specifies that the "side of the ditch nearest the crop must be straight, though it need not be more than 10 cm (4 in) deep. The worms cannot crawl up a sheer slope." In many situations, the plastic lining for the trench may not be necessary, and you could experiment with alternatives. (Scott Sherman used a cut-away PVC pipe buried at ground level to catch chinch bugs.) If you have field success with variations on these methods, please let us know.
James Gordley in Panama responded to this note on using trenches to control potato beetles. "I was experimenting with raising potatoes under different mulches. I would lay old carpet in my garden after working the ground in the spring. Every 30 cm I cut a slit in the carpet and inserted a seed potato. To my surprise there were no potato beetles on the plants growing through the carpet, while the plants in the next row (without carpet) had beetles on them. This was true for 3 years in a row. This method also produced potatoes 2 weeks ahead of my other plantings which were sown the same day. "Another method for beetle control is to run a handful of the insects in some water through the blender. Strain the juice and add 1/2 cup to 1 gallon of water. Spray this solution on the infected plants. Within 2 days there were no more beetles on the plants, and I saw many dead beetles on the ground. The 'beetle concentrate' can be frozen in small portions and then used as needed."
FLY CONTROL WITH MUSCOVY DUCKS. The Heifer Project Exchange quotes Jim Rankin in Togo. "People are seldom bothered by flies because they keep Muscovy ducks. For a fetish ceremony they killed a number of ducks. He opened the crops to see what they had eaten. Each one was filled with hundreds of flies."
BioOptions vol 1 page 6, 1990, also addressed this subject. Don Mock, extension livestock entomologist at Kansas State University says, "The Muscovy duck and the cattle egret may someday be enlisted as a major natural weapon of defence against the housefly and the horse and deer fly." A Canadian study with dairy calves showed that Muscovy ducks removed 30 times more houseflies than manufactured flytraps, baitcards, flypaper, or flysheets. The ducks also ate spilled feed, eliminating a fly breeding site.
FRUIT FLY TRAP MADE FROM BASIL. [The following is taken from a note in Ileia Newsletter, vol 9, # 3, p. 31.] "In Keralea (southern India) fruit fly (Dacus dorsalis and D. cucurbitae) incidence is severe in mango trees. P. Reghunath and M. Indira describe a low-cost technology to combat this insect pest."
A fruit fly trap is prepared as follows: "20 g of Ocimum sanctum (holy basil) leaves are crushed and the extract together with the crushed leaves are placed inside a coconut shell, which is then filled with 100 ml water. To increase the keeping quality of the extract, 0.5 g citric acid is added and the extract is then poisoned by mixing 0.5 g carbofuran 3G. The traps are suspended from mango tree branches at a rate of 4 traps per tree. The fruit flies feed on the ocimum extract and are killed in a few minutes. In our trial, over a hundred flies per week were caught in this way.
"To successfully control pests we advise an integrated strategy. Set the traps in the trees at the above rate, as soon as fruit set begins and continue till harvest. Change the traps every week and set fresh traps. When the population of flies is heavy, give a spray with malathion 0.1% and sugar 2%. Collect and destroy attacked fruits that rot and drop down."
CATCHING FLIES WITH VINEGAR AND HONEY. Jimmy Richardson in Australia wrote, "Your note on a fruit fly trap made from basil and insecticide prompts me to send the simple plans for the one that we use. The trap uses harmless ingredients VERY effectively against the fruit fly. To make the trap, cut two holes about 4 fingers high from the bottom in the side of a 2-liter container with a screw-on cap. To suspend the trap, drill a hole in the center of the cap, then push a double width of string through and knot on the inside.
"To make the attractant mixture, mix 1 cup of vinegar, 2 cups of water and 1 tablespoon of honey and shake well. Fill the trap to just below the holes with this mixture and hang the container about 5 feet high. Flies enter the container and fall into the attractant. I estimate it is 90-95% effective, and no poisons."
LEAF-CUTTER ANTS ARE A CHALLENGE TO MANY. Marianne Frederick contacted ECHO with a vivid description of problems of leaf-cutter ants in Guyana. She said that farmers even tried building water filled moats around plants but the ants built leaf bridges and crossed right over. She wonders if there are controls that do not involve commercial insecticides.
Dr. Keith Andrews at Zamorano in Honduras told us of a technique using freshly cut leaves of jack bean Canavalia ensiformis. The following comes from "The use of jackbean as a biological control for leaf-cutting ants" in Biotropica, vol 11(4) 1979 pp 313-14. Five to 15 kg of leaves were placed nightly on top of and around mounds covering an area of 25 to 100 square meters for three consecutive nights. All the leaves disappeared by the following morning, the ants apparently preferring them over the plants surrounding the colony ...[including citrus, cashew and mango trees]. A single three-night treatment usually resulted in complete cessation of ant activity for periods ranging from four months to five years (when observation ended). Infrequently, very small black ants (possibly forms of the same species) would appear 2-3 weeks following treatment of the colonies. Because of their random and disorganized activity, they were controlled with small doses of insecticide.
"It is presumed that the effect of jackbean on leaf-cutting ant colonies is due to the action of fungicides such as demethylhomopterocarpin contained in jackbean leaves on the ants' fungus gardens." The ants carry the leaves into the mound where they are normally transformed by fungal activity into the food upon which they depend. That's about all the article reported, and no data was included.
Tom Post had trouble establishing neem trees in Belize because of leaf-cutter ant damage. "They would strip whole trees. I planted jack bean around the trees. When the plants got about a foot tall all damage stopped. But there was no evidence that they were stripping jackbean leaves. In fact, we placed leaves on their trails and on the mound and ants would not pick them up. A project in El Salvador likewise found they would not pick up leaves spread on the trail or the mound."
Dr. Warwick Kerr in Brazil writes that "One recent research revealed that sesame, Sesamum indicum, protects the plantations against leaf-cutter ants, Atta sexden. The ants bring it to the ant hill and it stops growth of fungi."
Leaf-cutter ants are a serious problem. Let us know if you try jack bean or sesame control, or if you have another method. There are too many unanswered questions to recommend the method with much conviction. This would be a good research project for some of the scientists among our readers.
Alfredo Petrov in Cochabamba, Bolivia shared his experience in controlling leaf-cutter ants. "I work in a semi- arid valley, 2,700 meters above sea level. Leaf-cutter ants have defoliated our peach trees, rose bushes, potato fields and tree plantation seedlings. So they are not only a problem of the humid tropics.
"The best protection for tall plants with narrow stems, such as roses or young peach trees, is loosely-wadded sheep wool tied around the stem! Ants don't like to cross it and it is almost totally effective. Local sheep conveniently deposit the necessary tufts of wool on our barbed wire fences. This method is not practical for older trees with thick trunks or for tree nurseries with thousands of seedlings.
"For trees with thick trunks, merely whitewashing a section of the trunk with lime seems to somewhat reduce leaf- cutter damage. We mix the lime with mucilaginous cactus (Opuntia sp.) juice to help it stick on longer. Perhaps the black ants don't like to cross the contrasting white background, which makes their black march easily visible to predators?
"Several Bolivians have recommended wrapping fruit tree trunks with sticky tape, sticky side outward. I haven't found this to be very practical; in our intense mountain sunshine it doesn't last long - the tape soon dries out and turns brittle. There is a sticky liquid sold in the USA for painting on tree trunks to trap crawling pests called "Tanglefoot". Does anyone have more information on this? [Ed: This product is indeed very sticky, not affected by temperature or weather, and very effective at trapping insects until it traps a lot of dirt and no longer has a sticky surface. It does not dry out and can last several months. The price in one U.S. catalogue is $25/5 lbs-not exactly inexpensive; does anyone have experience with alternatives? See page 198 for description of using STP oil treatment as a substitute.]
"One local person suggested that I protect prized plants with a circle of sugar poured on the ground around the stem. I don't know why this would work, and haven't been desperate enough to try it yet. One successful elderly farmer has effectively protected his potato field with a barrier strip of organic debris taken from distant ant colonies. Presumably the ants avoid the smell of ants from other ant colonies.
"The other philosophy is to find the local ant colonies and kill them, instead of protecting the plants directly. This is usually done by sprinkling powerful insecticide powders around the entrance holes, a practice to which I am ecologically opposed. Since human urine contains a fungicide, I tried attacking a colony's fungus garden by pouring urine down the entrance hole. It did get rid of the colony, but took several applications a day for eight days-too much trouble for more than one colony."
Marsha Hanzi in Bahia, Brazil wrote that leaf-cutter ants are the "janitors" of a forest ecosystem. They remove weak plants and produce compost richer than worm castings, enriching the soil and preparing it to support trees. "These ants dominate the scene where most organic matter has been removed [so] if we increase the amount of organic matter on the ground (by planting leguminous trees and pruning them every two months during the rainy season), the leaf-cutters go back to cleaning out the system without serious damage to our crops and trees.
"This I can affirm from personal experience; in the first year of my permaculture system, on hardened poor clays, the ants cut everything I planted. Today, three years later, they still exist, and sometimes nibble something, but normally go next door and cut the neighbor's plants! (His soil has very little organic matter.)"
To begin building a system in highly degraded areas with leaf-cutter ants in a balanced role, she recommends planting local pioneer plants every meter and pruning them frequently to build organic matter and restore soil fertility. Bananas can also be used, three meters apart. Then she looks for leguminous trees adapted to the area; Marsha has not lost leguminous trees to ants. She uses native Ingas, Erythrina, and Gliricidia in the humid and transitional zones and plants food plants among these species. In transitional zones, she has seen cashew and guava trees growing in ant mounds; perhaps their thick leathery leaves make them less prone to attack.
One creative idea for keeping the ants off new plantings is to distract the ants by planting "enormous quantities of pigeon pea (Cajanus cajan), which has incredible resprouting capacity if eaten by the ants. Ants prefer the flowers of these to practically anything else other than, perhaps, young citrus trees, which need to be protected. Although planting sesame does work, killing the fungi which feed the young, I prefer to feed the ants and not kill them" for their long-term benefits to the soil. She also suggests that guinea fowl and chickens might help control the ant population in outbreak situations. She welcomes correspondence at: Instituto de Permacultura da Bahia, Condomínio Aguas Finas QE L4, Lauro de Freitas, Bahia, BRAZIL, CEP 42700-000; fax 55 71 378 1520.
FALLEN ORANGES FILLED WITH INSECTS. Jiwan Dewan in Nepal wrote that half of his navel orange fruit was dropping and was filled with maggots. I called Dr. Carl Campbell for help. Carl said this is a tough one to figure out, but here are some thoughts. The first step is to determine if the insects are causing the drop or if they are a secondary cause, entering after some other problem. The letter did not say at what stage they dropped, whether as very young fruit or more mature fruit. If it is the mature fruit that is dropping, then it is perhaps more likely that the problem is directly caused by eggs laid in the fruit.
Fruit drops are very serious some years in Florida. It turns out to be due to the fungus anthracnose that is attacking the blossoms combined with both thrips and midges feeding on the ovaries of the flowers. A careful look at the blooms will show if there is either fungus or insect damage. It could be that a fungicide at bloom time would solve the problem. Another common cause of fruit drop is dry weather. If it does not rain at least an inch a week one should irrigate (if that is a possibility). Citrus is very sensitive to lack of water.
It would help to know whether it is fly, beetle or lepidoptera larvae in the fruit. Here is a rough way to tell. Fly larvae have no legs, whereas both beetle and lepidoptera larvae do. Beetle larvae "look like grubs." Lepidoptera larvae tend to be longer and slimmer than beetle larvae and somewhat flattened.
If the fallen fruits are of a good size, see if there are any obvious puncture wounds. In the equatorial tropics an adult fruit-piercing moth causes a lot of problems in citrus. Usually no one even knows the moth is around. It pierces the fruit and sucks juice at night, then quickly leaves. What most people see is the fungal lesion that develops around the spot.
MEALYBUG CONTROL. In 1991, Wayne Teel in Mozambique asked about controlling cassava mealybug (Phenacoccus manihoti) without commercial insecticides. The mealybug destroyed up to 80% of the cassava crop.
Natural Crop Protection says that cow urine is used against mealy bugs, thrips, mites, and other insects in Sri Lanka. Cows are penned overnight on a concrete floor which slopes to a tank. Collected urine stands exposed to sun for 2 weeks, then is diluted with 1-6 parts water and applied to plants. Tender vegetables require a more dilute urine solution than fully grown trees, as too concentrated a solution can burn the leaves. Test dilutions on different plants.
The 1995 World Food Prize was awarded to Dr. Hans Herren for his successful efforts in finding and implementing the biological control of the cassava mealybug in Africa. Based at Nigeria's International Institute of Tropical Agriculture, Dr. Herren coordinated the worldwide collaboration (1979-1992) which resulted in mealybug control in 95% of the cassava-growing zones of Africa. Researchers found natural enemies in the pest's South American home, and tested them in Africa. The most successful was the parasitic wasp Epidinocarsis lopezi, which was released in Nigeria in 1981. This wasp has been dispersed and established throughout Africa. We hope it has reached Mozambique by now.
LEUCAENA PSYLLID OUTBREAK AND CONTROL. Pest outbreaks can be sudden and devastating. After years of promoting Leucaena leucocephala for erosion control on hillsides and an important tree in agroforestry systems, the psyllid became a serious problem in Asia in 1986. Control efforts included screening for psyllid- resistant leucaenas and introducing parasitic wasps for biological control. This "story" illustrates many important principles of plant protection and pest control: avoiding dependency on just a few species and achieving a balance between pest and predator insects. Below, you can follow the development of solutions to this problem.
FROM MARCH 1986: INSECT PEST CAUSING SERIOUS DAMAGE TO LEUCAENA PLANTINGS IN THE PHILIPPINES. Five of our readers in the Philippines have written about this problem. It is a good warning to others also that there is always danger in planting incredibly large areas to one species. The Nitrogen Fixing Tree Association (NFTA) has published a two page analysis of the problem. It is caused by psyllid insects (Heteropsylla spp.) or jumping plant lice, which have spread rapidly around the world in the past few years. The insects are native to the Caribbean and eastern Mexico, where they seldom cause severe damage because of natural predators. This suggests that introduction of predators [or even gradual natural build-up of local predators?] may be the best control. Some ladybird beetle larvae are outstanding predators, e.g. Curinus abdominalis. The insects are not spread by seeds. The most likely methods include high-altitude air movements, cargo in airplanes, or illicitly shipped live plants.
What can we learn? I would be hesitant to rely exclusively on one species of tree for a particular purpose. Leucaena may outperform most trees in your setting, but other species have exceptional qualities as well. In the long run, a mixture is better. Also, you can plant more than one variety of leucaena. Folks who write to ECHO for seed are sent four leucaena varieties for this very reason. Readers who are heavily involved in reforestation should receive the NFTA bulletins on a wide variety of species with potential for their area; write Winrock International, Petit Jean Mountain, Rt. 3, Box 376, Morrilton, Arkansas 72110-9537, USA.
FROM OCTOBER 1993: PSYLLID-RESISTANT LEUCAENA. We asked Mark Powell at the Nitrogen Fixing Tree Association what Leucaena leucocephala variety he would recommend where psyllid insects are a problem. He sent us a variety called K636, the top performer in their 'New Giants' trial at Waimanalo, Hawaii. "Although this variety has performed well especially after it achieves heights above 5 meters, it will support large psyllid population buildup which can defoliate all juvenile leaves. It has been observed that it tends to retain its older leaves during periods of high psyllid pressure." The K8 variety was one favored giant type several years ago, but it is now "disfavored due to its relatively high susceptibility to psyllid defoliation."
FROM JUNE 1992: LEUCAENA PSYLLID IN AFRICA. Mike Benge with USAID tells us that the leucaena psyllid that had such a devastating effect on leucaena trees in parts of Asia (e.g. Philippines) has reached Africa. It has been identified on the islands of Mauritius and Reunion. ICRAF and the CAB International Institute of Biological Control (IIBC) are coordinating the design of a strategy for biological control of this pest. Host- specific parasitic wasps found in the Americas as well as other natural enemies are bringing it under control in Asia. "In situations like this I do not believe that resistant varieties are the best answer. People should be cautioned not to lay too many hopes on resistance as breeding takes a long time and insects adapt so quickly and so well. They are like people, when sirloin isn't available anymore they'll eat hamburger."
IN 1995 AND 1996, Mike Benge with USAID gave us an update on the damage to leucaena trees by the psyllid insect in Asia. "The introduction of the parasitic wasp seems to have reduced the damage to a somewhat acceptable economical level." "The biocontrol of the psyllid in SE Asia has gone well with the host-specific parasitic wasps Psyllaephagus yaseeni and Tamarixia leucaenae (the region); ladybird and ladybug beetles Olla abdominialis and Curinus coerulus (particularly in Indonesia); and other naturally-occurring [controls] such as spiders." "A survey in the Philippines conducted by Winrock...determined that leucaena is still the tree of choice by farmers. The leucaena systems heavily damaged in the past are recouping and are productive again in most places. As you know, the psyllid has spread to Africa, and there is now an effort to introduce the parasitic wasps there...the IIBC in England is involved."
USING GRAPEFRUIT TO CONTROL SLUGS? The "Letters" section of Organic Gardening Magazine contained the following suggestion. The writer lived in Oregon where she was "surrounded by slugs." She tried oyster shells, rough bark dust, rosemary, hunting them down and sprinkling salt on them and beer baits, and found them all inadequate. "Then I discovered grapefruit. After you've used the pulpy insides for breakfast, set the rinds (with a little pulp left) upside down igloo-style around your garden." She says that the slugs will hide underneath the grapefruit and die. We have no slug problem at ECHO, so we cannot verify this technique. If you do, please let us know whether it worked. This seems too good to be true, but it would be wonderful it is does work.
IRON SULFATE MOLLUSCICIDE. The horticultural newsletter HortIdeas (September 1990 and April 1992) has reviewed several reports on using iron sulfate (green vitriol) to control slugs. "Recent laboratory trials in England support the notion that iron sulfate is rapidly absorbed by slugs which contact it and is highly toxic to slugs. ...Iron sulfate is cheap, easily available, and not very toxic to humans." In fact "it is a widely prescribed iron supplement for people suffering from anemia."
A subscriber in Spain, Brian Lynas, reports great success by spraying or sprinkling (especially following rain) a solution of iron sulfate. "For over a year I have intermittently sprayed iron sulfate solution around lettuces, brassicas [Ed: cabbage family] and any other plants which were under attack from mollusks. The concentration does not seem to be critical. I use four heaping teaspoons in a five-quart sprayer (twice that concentration if using a watering can) on the soil around slug-attracting plants. ...I've sprayed the soil and also sprayed the plants directly. There's no doubt that either is effective, especially if you can directly spray the mollusks themselves.
"The spray seems to act as a contact poison, so if the animals are wetted or have to cross a sprayed area like a leaf, they die. Unfortunately, when sprayed onto soil, the soluble iron sulfate is quickly changed to insoluble hydrous iron oxides and is ... inactivated.
"Iron sulfate burns some sensitive (usually young) plants. The damage is minor, and my impression is that the anti-mollusk benefit far outweighs the disadvantage. In fact, ferrous sulfate solution at around 3% strength is often used for correcting iron deficiencies by direct spraying on foliage.
"Regular spraying-especially after rains-around the plant bases where the creatures hide, as well as generally around the cultivated area, dramatically decreases the mollusk population with almost immediate effect. [In Mallorca] a small conical snail occurs by the hundreds of thousands. A couple months ago these were infesting a patch in which I'd planted small brassicas and lettuces. Sometimes each plant would have 30 or more snails lying around underneath. I sprayed the solution over them, and they evidently all died. What's more, it seems this killed ... the eggs also, for even now there are practically no mollusks in the area."
GARLIC TO KILL SNAILS? Drs. D.K. Singh and A. Singh at the University of Gorakhpur in India looked at the molluscicidal properties of an extract of common garlic, Allium sativum. Aquatic snails, Lymnaea acuminata, an intermediate host for parasites which cause fascioliasis of cattle, were used in the experiment. Ten snails were placed in each aquarium. The required amount of garlic cloves was minced in 5 ml water, homogenized for 5 minutes [in a blender], and centrifuged at 1000 g for 10 minutes and added to the water. [Ed: For other than experimental use, this procedure could be greatly simplified; e.g. filtering could probably replace centrifuging.] Each experiment was repeated six times. Concentrations are expressed as weight of garlic clove per liter.
The LC50 value (the Lethal Concentration required to kill 50% of the snails) was both dose and time dependent. Thus with an increase in exposure time, the LC50 of garlic decreased from 55 mg per liter at 24 hours to 30 at 48 hours and 12 at 96 hours. The LC90 (the concentration to skill 90% of the snails) at 96 hours was 36 mg garlic.
How does this compare with commercial molluscicides? The 96 hour LC50 of two synthetic molluscicides is higher (i.e. less effective): phorate is 15 mg and carbaryl is 14 compared to 12 for garlic. However, the standard molluscicide niclosamide has five times higher toxicity in 24 hours (LC50 = 12 mg) than garlic (55 mg). The authors believe that if the active ingredient were further purified, it would probably be more toxic than the best synthetic.
NEEM LEAF TEA TO CONTROL TERMITES. We seldom hear of any natural control that works with termites. Don Mansfield in Mali sent the following. "A Norwegian missionary here in Mali told me how to control termite damage to trees with neem leaf tea (Azadirachta indica). A barrel or bucket is filled with green neem leaves. They cover the leaves with water and after 4 days use the liquid against termites. I don't know whether it kills them or just keeps them away. The missionaries swear it really works.
"It has been a great success for me. Most of the time when I've used it, it has been setting for at least 2 weeks. When I see where the termites are starting up a tree or pole, I knock them and their clay off. Then I take a paint brush and paint the whole area where the termites had been on with the tea. I make sure that plenty runs down around the base. Twice I have had to do it a second time after about a week, but all the other times I have only done it once and the termites have not come back. It has been 5 or 6 months since I treated a few mango trees, and they have not been bothered since."
TERMITE-RESISTANT TREE reported by Roland Lesseps, S. J., in Zambia. "Termites here make it very difficult to establish tree seedlings in the field. In some places at Kasisi we have lost about 90% of our Leucaena leucocephala seedlings. So we are always on the lookout for a tree that is termite resistant. An excellent one is Senna (Cassia) siamea. We planted four rows four years ago (about 70 trees per row) in a field terribly infested with termites. Almost all the trees are alive and growing luxuriantly. We have coppiced them three times and used the leaves in compost piles. The cut branches make good poles or firewood. We earlier fed the leaves to cattle, then we heard at an ICRAF meeting that the leaves, though eaten by goats, are not good for cattle."
SUGGESTIONS TO HELP AGROFORESTERS REDUCE SEEDLING LOSSES FROM TERMITES. [Taken from Agroforestry Today, July-Sept. 1990 pp 4-6].
1. Select trees that are resistant to termites. These include species of Cassia, Acacia, Grevillea, Markhamia, and Terminalia.
2. Use plant extracts and minerals as protectants. These include finely chopped leaves of Euphorbia tirucalli or wood ash applied to planting holes; leaf or berry extracts of Aloe graminicola, Melia azedarach [Ed: Chinaberry, a freeze-tolerant relative of neem], Lippia javanica or Ocimum sp. (basil); and leaf mulches of Cassia siamea or Azadirachta indica (neem).
3. Plant extra seedlings, to allow for termite losses, both in the nursery and after planting out.
4. Use containers of polyethylene tubing. Pots made of banana fibre should not be used for seedlings where termites are a threat. It is of paramount importance at transplanting to remove the plastic sleeve carefully and retain an intact soil-root ball.
5. Use healthy and vigorous planting stock. Any root pruning should be scheduled to allow sufficient recovery and repair of damaged tissues before transplanting.
6. Give nursery stock enough water just before planting out.
7. Plant seedlings on time, soon after the first annual crops are sown or when the soil is wet to a depth of 20-30 cm.
8. Provide substitute food sources for termites. This could involve leaving as much cleared plant debris as possible on the soil surface when preparing tree planting sites; using organic manure in planting holes; ring weeding rather than clear-weeding stands of young seedlings; retaining grass residues as mulch in and around planting holes; and placing a row of cut banana pseudostems along nursery perimeters.
9. Apply spot treatments of a controlled-release granular formulation of carbosulfan (0.3 to 1.0 grams active ingredient per plant). Other non-persistent insecticides such as chlorpyrifos and carbofuran are not recommended due to severe phytotoxic effects.
Research is currently in progress on another novel approach to control of subterranean termites [which rely on fungi to make suitable food from decaying vegetation carried into the colony]. This approach is to apply fungicides to deprive them of their major food source by controlling these symbiotic fungi.
ARE BRUCHID BEETLES THE SAME AS WEEVILS? We have mentioned using cooking oil to control bruchid beetles in stored seeds. We were asked if they are the same as weevils. Good question. The answer is yes. Quoting from Insect Life, "There are two general groups of seed borers: species that feed in green or living seeds and those that attack dry seeds. The [former] deposit eggs in the seeds by means of a long ovipositor that penetrates the flesh of the fruit. The adults usually emerge after the fruits have decayed. The latter, the common feeders upon dried seeds, are known as weevils." Several generations can develop in a container of stored seeds.
SHORT-TERM HEATING KILLS COWPEA WEEVILS. The January 1992 issue of HortIdeas reports that two Purdue University entomologists have developed an extremely low-cost technique for ridding dried cowpeas of weevils (Callosobruchus maculatus). If you have some clear plastic, a piece of dark cloth, a few rocks, a semi- sunny day, and about an hour, you should be able to eradicate the weevils in a few pounds of cowpeas.
"A simple solar heater was made by placing a 3 ft x 3 ft (1 m2) black plastic sheet on the ground, adding 1 kg (2.2 pounds) of cowpeas (spread out only one layer thick), and adding a cover of clear plastic sheeting, held down at the edges by rocks. It was discovered that the ambient temperature doesn't affect the temperature inside the solar heater very much on clear or bright-hazy days; the temperature inside cowpeas within the solar heater was 149 F 15 minutes after exposure began on a slightly hazy day at noon."
After solar heating for different times, the numbers of beetles emerging were counted (time in minutes followed by numbers in parentheses): 0 (227 adults), 30 (12 adults), 60 (2 adults), 120 (no adults), 180 (no adults). The treatment did not significantly alter either cooking times or germination percentages. The seeds did lose water, which was probably beneficial. Different types and colors were tried for the sheet on the ground (including cloth) and seemed to make little difference. This time, in all cases no adults emerged after a 45-minute treatment.
SWEET POTATO WEEVIL PROBLEMS. Matt Huber wrote from Haiti, "An insect is severely damaging the roots of sweet potatoes. What can be done?" He sent us a jar containing several of the tiny worms (a few mm long) in alcohol. Dr. Frank Martin identified them as sweet potato weevils, and made these recommendations for their control. It is very important to plant where sweet potatoes have not grown for about a year. It is also important to keep any wild relatives of the sweet potato from the field (e.g. morning glories). When cuttings are taken to start a new planting, soak them for up to 24 hours in a 1% solution of a systemic insecticide. One such insecticide is furadan. This will prevent introduction of the weevil into the new field.
He mentioned that the tubers are damaged extensively. Frank said that the observation that there is this much damage most likely means that farmers are using a long maturing variety [or are "storing" them in the field, harvesting as needed]. Sweet potatoes differ widely in time required for maturity. Matt needs to search for some short-maturing alternatives. In the meantime, harvest as early as possible.
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