MOFGA Pest Report 2005
9 July
(View List Of All 2005 Pest Reports)
Mexican Bean Beetle - (Epilachna varivestis)
Mexican bean beetle levels are variable on some farms from year to year, and regular pests on others. I have just seen them appear this year. Here is a piece (that I modified for organic growers) from an Extension Bulletin in New York:
Injury: The Mexican bean beetle, formerly called the bean ladybird, is one of the most destructive insect pests of beans in New York State. The beetle feeds on the leaves of almost all types of beans including snap, lima, pinto, navy, kidney and soybeans. With snap beans, bush varieties seem to be attacked more readily than pole varieties.
Most of the damage from the Mexican bean beetle occurs during July and August. Both the adult and the larval stages feed on the foliage, chewing out holes in the leaves. They usually feed on the undersides of the leaves and sometimes will attack young pods and stems. As a result of the feeding, only the veins are left giving the leaves a lacy appearance. Yield may be greatly reduced and the entire planting may be destroyed in severe infestations.
Description: The Mexican bean beetle is a convex beetle, about 1/3 inch long, and pale yellow to copper color with 16 black spots on its back. The beetles are pale yellow when the first emerge from the pupal stage, but as they age, they develop the typical copper color. The eggs are yellow and found in irregular clusters of 40 or more. The larvae are also yellow and have spines with branches on their body giving them a fuzzy appearance.
Life History: The adult beetles overwinter in sheltered locations. They leave the overwintering sites when the weather warms up in mid-to-late spring. The females deposit their yellow eggs in clusters on the undersides of the bean leaves. In 5-14 days the young larvae hatch and begin to feed, passing through four molts before reaching the mature size of about 1/3-inch in 3 to 5 weeks. The mature larvae attach themselves to the undersides of the bean leaves and transform into the pupal stage. The pupal stage is the resting stage and does not feed. In 3 to 7 days the adult beetle emerges. In the fall when cold weather approaches, the adults migrate to sheltered areas in which they will spend the winter.
Management: Sanitation is important since the beetle spends the winter hiding in sheltered areas. Plow under beans after harvest. Clean up plant debris around the fields. Rotate to new fields as far away from bean fields as possible.
Handpick beetles and eggs in small plantings. Plant early to avoid this pest. Planting the heaviest crop of beans early in the season may be helpful in eliminating some of the beetle damage because the beetle populations are heaviest during the mid-to-late summer period.
Apply neem (repels beetles) or pyrethrum as needed. Wait one day before harvesting. Before using any pesticide, check the label. Both the crop you wish to treat and the pest you are treating for must be listed on the label. If not, do not use the pesticide. Although dry beans are on the Entrust label, Mexican bean beetle is not. I have not heard any reports of Entrust being effective against the bean beetle either. I have heard from one grower who used Entrust on beans (for some other pest) and reported no bean beetle damage, but it was unclear whether it was a year with little damage from them or the Entrust helped.
4/78 Originally Prepared by: Carolyn Klass, Senior Extension Associate, Cornell University; and Arthur A. Muka, Department of Entomology, Cornell University; 1/89 slightly revised
PEPPER POLLINATION, FRUITING, HARVEST AND STORAGE
(adapted from Michelle Infante-Casella, Rutgers Extension, Reprinted from Vermont Veg and Berry News)
It’s not uncommon for pepper plants to flower but fail to set fruit. Flowers that do not pollinate properly may abort, creating a yield loss. If temperatures are too high during flowering, or if other adverse weather conditions occur, flowers may abort due to plant stress. Once flowers are pollinated and fruit begin to form the plant starts to use more water and nutrients, so irrigation and fertilization are key at this time. Also, fruit should be protected from insects and diseases that may make them unmarketable.
As fruit develops it creates stress on the plant because of the “source/sink” relationship in plants. When a plant begins to grow, the growing tips act as a “sink” that demands the most water and nutrients and is the primary growth area. The older leaves are the “source”, since they are actively photosynthesizing (producing energy) and would be first sacrificed if the plant were under environmental stress. This is why when a plant is under drought stress, the lower leaves may wilt and yellow first and fall off sooner, due to water and nutrients being diverted to other areas of the plant. When flowers or fruit form, they become the “sink” and the leaves, roots, and stems of the plant are their “source” of energy, water, and nutrients. Plants under stress will form flowers, and set fruit to make seeds in order to continue the next generation. This is a survival mechanism, and it explains why stressed, root-bound, sickly looking transplants left over in greenhouse trays will form fruit, even when the plant is very small. Therefore, if you remove pepper fruit, you remove the “sink” and allow energy, water, and nutrients back to produce more leaves, stems, flowers, and ultimately, more fruit.
Thus, timely harvests of bell peppers can help maintain production through the season, which can sometimes extend into fall with the help of row covers or mild weather conditions. Bell peppers are typically harvested at 10 to 15 day intervals for green peppers. If red peppers are desired due to higher prices or market demand, fruit must be left on the plant. From the time a green pepper reaches its final size it will take about 10 days for it to become fully red. When peppers are left on the plant to turn red, this adds more stress to the plant and physiologically promotes senescence (the gradual death process), so it makes sense to harvest for green fruit early in the season and only leave fruit to turn red after the plants have been harvested several times.
Peppers should be harvested during cooler parts of the day when field heat is minimal and quickly placed in cold storage to increase shelf life. Peppers are sensitive to chilling injury and are best stored at 45o-55o F with 90-95% humidity. Temperatures below this may cause pitting or softening of the tissue. Also be sure to not store peppers with ethylene-producing fruit. This will also shorten the shelf life and may cause discoloration of the peppers.
KEEP AN EYE OUT FOR POTATO LEAFHOPPER
(reprinted from Vern Grubinger's Vermont Veg and Berry News)
Potato leafhopper injury is expected to be found soon in most locations They recently already arrived here in Brattleboro, dropping down as storm fronts pass through. This insect commonly attacks alfalfa, beans and potatoes, although it also can damage melons, strawberries, raspberries and other crops. Symptoms include yellowing, stunting and curling leaves. On bean plantings that have had severe PLH feeding symptoms may look like virus infection. To scout for PLH, walk through your fields and lightly brush plants in different locations. When disturbed, the small, whitish adults can be seen flying off plants. Then look for small, light green leafhopper nymphs on the underside of the leaves. They are about 1/16th inch long and bullet-shaped. Don’t wait until you see clouds of adults flying around – start scouting for them now. The IPM threshold for PLH is quite low. Late maturing potato varieties including Katahdin, Elba, Green Mountain, Kennebec, and Blossom have some resistance, and likely will not need spraying. Yukon Gold, Red Norland, and most other varieties, are very susceptible. Check the New England Vegetable Management Guide for appropriate pesticides.
BRASSICAS: CATERPILLARS AND FLEA BEETLES
(reprinted from UMASS Vegetable Notes)
Its not news that diamondback moths (DBM) and imported cabbage worms (ICW) are active in brassica fields. Growers should be scouting for these pests. Cabbage loopers (CL) have not been reported yet but could also be present. When scouting for 'worms', be sure to look beneath the leaves and on the inner most portions of the plants. Look for feeding damage as well as for caterpillars.
Tiny feeding holes are often easier to spot than small green caterpillars. Apply controls when thresholds are reached, and direct materials at the undersides of leaves as much as possible. Use at least 50 gal/A of water to achieve better spray coverage, and use a spreader-sticker.
A threshold of 15%-infested plants (an 'infested' plant has at least one caterpillar of any species) is recommended for any heading cabbage, broccoli, and all leafy greens. Before the cupping stage, in cabbage and broccoli, use a threshold of 35% plants infested. These thresholds provide a clean crop at harvest. Cauliflower use a 10% threshold. An excellent comparison of "worm" insects at various life stages can be found at this NCSU web page (click on images to enlarge).
Imported Cabbageworm: The larva is a slow-moving, velvety-green caterpillar, which grows through a series of five stages, or instars, to a length of 1 1/4 inches. Larger caterpillars have a delicate yellow line that runs lengthwise down the center of their bodies. Small larvae feed on the undersides of outer leaves after hatching. Larger larvae are more mobile and are often found in the florets of broccoli or feeding on the heads of cabbage. Larvae may also move to neighboring plants.
Diamondback Moth larvae grow through four instars to a length of 1/3-inch. They are light green; tapering to points on both ends and appearing scalloped or segmented along the edges of their bodies. During the first two instars, the larvae have black heads, which later lighten to match their green bodies. They can be distinguished from other caterpillar pests by their habit of wiggling frantically when touched or disturbed. They may also drop from the plant and suspend themselves on a silken thread until the disturbance passes. The larval stage lasts from two to four weeks, depending upon temperatures. Pupae are found attached to the undersides of crop foliage and appear to be thinly veiled under a fine, net-like silken cocoon.
The cabbage looper caterpillar is light green, with wavy white or light yellow lines down the back and sides. Fullgrown larvae reach 1 1/2 to 2 inches. At rest or when disturbed, cabbage loopers of any size will raise the middle of their body in a characteristic "loop" shape. Eggs are round, light green or yellow, and laid underneath the foliage. Feeding tends to create ragged, large holes in foliage, on both frame leaves and heads. Moths arrive in New England on migratory flights from the South, like corn earworm.
Insecticides for Caterpillars: In the area of caterpillar control there are many products available. Spinosad (Entrust), and both Bt aizawi (eg Xentari, Agree) and Bt kurstaki ( eg Dipel, Biobit) products work well; Bt aizawi is recommended when diamondback moth is the dominant species. It is possible to get excellent control of the three major caterpillar pests using low-risk products that are safe to handle and conserve beneficial insects (which do have an impact in suppressing aphids and caterpillars). It is also easier now to rotate among different types of products, to prevent selecting for resistance to any single product.
Flea beetle numbers have gone down - it is likely that we are between adult generations - pupae and larvae are in the soil, near the roots of early brassicas. We are starting to see an increase in numbers of striped flea beetles, which emerge a bit earlier. Planting fall broccoli or greens? Think twice before you put them close to your spring plantings - especially if you had a significant number of flea beetles. Those new adult beetles that will be emerging in late July and early August will be very hungry. If your fall brassicas are close by, feeding damage will be heavy. Try to rotate fall brassicas to a field that did not have spring brassicas.
(About the author: Eric is MOFGA’s Technical Services Director, essentially an organic "extension agent". He can be reached at the MOFGA office to answer your questions about farming and gardening. Link to MOFGA Contact Page, or email Eric directly.)