Pest and Disease Update May 20, 1999

CROP CONDITIONS
FLOATING ROW COVERS
PESTS:
CRUCIFER
STRAWBERRIES
RASPBERRIES

A good portion of the information presented below has been taken from two publications created in Massachusetts for IPM production and modified for conditions in Maine and to meet the guidelines for organic productions. The two publications are the UMass. Veg. IPM Newsletter (Ruth Hazzard) and the Massachusetts Small Fruit IPM Message (Sonia Schloemann). For information on how to get these original publications contact me.

An April that logged the lowest or second-lowest rainfall in over 100 years had its advantages: even heavy fields could be worked early, and spring planting has been steady and uninterrupted. Dry conditions have in some cases slowed germination and growth, but many crops are ahead of schedule. Some crops such as peas are showing nitrogen deficiencies (yellowing leaves) due to the dry conditions, if they have not received irrigation.

ROW COVERS FOR PEST CONTROL AND EARLY YIELDS

If you have a diversified vegetable and/or berry operation, floating row covers can be a cost-effective and convenient tool for producing early, high-quality crops. Floating row covers provide significant growth enhancement by raising air temperature during the day and moderating cold temperatures at night and by reducing wind and heavy rain damage, while allowing light and water to penetrate to the crop. The result is earlier harvests and in some cases higher total yields. While it is not recommended to use them solely for frost protection, they do provide several degrees of protection when temperatures dip just below freezing. Lighter covers may give 2-3 degrees of protection, and heavier covers provide 4-8 degrees. A key benefit of the covers is that they exclude a wide range of insect pests which move into their host crop from outside the field.

Floating row covers are flexible, transparent fabric composed of spun-bonded polyester or polypropylene. They "float" directly on the surface of the crop, rising up as the plants grow. Edges are usually held down with soil, but weights such as earth-filled bags or rebar could be used.

Which type to use? There are several different weights, measured by the ounces per sq. yard. Materials that are 0.5- 0.6 oz/yd2 (e.g., Reemay, Agrofabric Pro 17, Covertan) provide growth enhancement and insect control, have high light transmission (85-90%), and are less expensive than heavier materials, but are more likely to rip from wind or sharp objects (fingernails, boots, deer hooves, stakes, and the like) One can expect about 1 ½ seasons of use out of these. Row cover that is 1.25 oz/ yd2 (Typar 518) is heavy enough to be more tear resistant, has good light transmission (70%) and is light enough to float over young plants. This type can last three seasons. Though more expensive than lighter fabrics, this type probably provides the most efficient cost per acre per year. The heaviest covers are >1.5 oz/ yd2, have lower light transmission (30-40%), are

used mainly for frost protection, and are durable enough to last for several seasons.

Support. Many crops can handle floating covers without any support—lettuce, greens, crucifers, onions, vine crops, potatoes, strawberries, sweet corn. Those with a tender, exposed growing point (tomatoes, peppers) should have some support to prevent damage from wind abrasion. Wire hoops provide good support, or short stakes if they are covered with a smooth top to prevent tearing.

Widths. Row covers can be purchased in widths ranging from 3 to 60 feet, and in lengths of 20 to 2550 feet. Wider covers are more labor-efficient because they have less edge to bury per covered area—but don’t try to lay them in a strong wind! Watch for weed growth under the cover—they provide a good environment for weeds, too. The cover may need to be rolled up to one edge for cultivation, then replaced—not as difficult a task as it might seem.

Storage. Row covers should be stored out of sunlight as soon as they are removed from the field. While many have been treated to reduce UV degradation, they will last longer if stored carefully out of light. Fold or roll covers in systematic way, so that they can be easily unfolded for the next use.

Insect Control.

Use covers on rotated fields, because some insects overwinter in the soil and could emerge under the cover. Also, seal the cover immediately after planting. If you need to pull it back for cultivation, do this when insects are less active—such as a cloudy day, or early morning.

Insects which are excluded by row covers:

Cabbage root maggot fly on spring or fall crucifers. Eggs are laid at the base of the stem by first-generation adults, which fly from late April to mid May. Maggots feed on roots and kill early cole crop seedlings. Row covers are a very effective control.

Flea beetles. There are many different species of flea beetles, each with a specific host crop. Because they typically spend the winter as adults around field edges, they can be effectively excluded by row cover, as long as the cover is placed on soon after planting. Crucifer and striped flea beetles, tiny black or striped beetles, cause shot-hole feeding on any of the cabbage family crops. Covers can be used in spring or fall on transplants, or all summer on direct-seeded crops, but are too hot for transplants in midsummer. Potato flea beetle causes similar damage to eggplant, tomato, and potato. Corn flea beetle also causes feeding damage but is a concern primarily because it vectors Stewart’s wilt. Excluding beetles prevents infection of young corn with this bacterial disease.

Spinach leaf miner in spring spinach, beets and chard. This slender black fly emerges from overwintering sites in the soil, and lays small, thin eggs side by side on the underside of leaves. Maggots tunnel inside the leaf, making unsightly pathways that render greens unmarketable. By keeping the flies off, covers prevent feeding damage.

Striped cucumber beetle on melons, summer squash, cucumbers, winter squash, and pumpkins. Row cover prevents feeding damage and transmission of bacterial wilt, which is vectored by the cucumber beetle.

European corn borer, which emerges in late May or early June and lays eggs on early corn. If row cover is left on into mid -late June, after first flight has peaked, it provides excellent protection. If removed just as flight starts (e.g., first week of June) the larger, healthy corn may be just as infested as corn that was never covered. Can be left on till tassel if enough slack is left for 3-4 feet of growth.

Colorado potato beetle, which moves into potato and eggplant in late May and early June. Covers should be removed before tuber initiation, which usually coincides with flowering, to prevent excessive heat.

Suppliers: American Agrifabrics, GA (800-565-5151), KEN-BAR, Inc., MA (800-336-8882 or 781-944-0003), Peaceful Valley Farm Supply, CA( 916-272-4769), Johnny’s Selected Seeds, ME (207-437-4395), Rain-Flo Irrigation, PA (717445-6976), Suntex CP, Inc, FL (941-706-0008 or 888-Suntex1) This list is not intended to be comprehensive and does not imply endorsement of the products of these companies nor lack of endorsement of others. Check your local supplier who may also carry floating row cover.

• R. Hazzard, using information from Otho Wells, University of New Hampshire

CURRENTLY FOUND OR SOON TO COME PESTS

Cabbage root maggot flies are now active or soon will be and laying eggs on early crucifer transplants. These flies overwinter in the soil as oblong, brown pupae, and emerge in late April. Flies are black, delicate and about ¼ inch long. Females lay eggs at the base of stems of crucifer plants, and the white legless maggots feed on the roots, causing the plant to wilt and die. Wilting can occur suddenly on plants that appear completely healthy and strong. Cabbage, broccoli, bok choi, Chinese cabbage, radish and other brassicas should be protected by using floating row covers. If the number of eggs reaches or exceeds an average of one egg per stem, significant crop damage can result.

In Maine this pest is usually only a problem for early crops (in the field before June 1).

On certain farms in southeastern Mass, eggs were found at high levels—averaging 10 or more eggs per plant. In the Connecticut Valley, some fields have been over the threshold of 1egg/stem, and some just below (running about 0.6-0.7 eggs per plant). No hatched eggs have been observed yet (May 13), but eggs have been present for over a week so maggots could be found soon on untreated crucifers.

To check your field for eggs, look for the 1/8-inch long, rice grain-shaped white eggs that are laid along the stem, or on the soil next to the stem of young transplants. Often eggs are laid in neat rows, or inserted into the soil. They may be under a small clod of dirt near the stem. A pencil point helps stir the soil to look for them. The number of eggs per stem can range from 1 to more than 20. The recommended scouting method is to check 40 plants in the field, in 10 groups of 4. If you find more than an average of 1 egg/stem, it is likely to be a damaging population.

There is no organic solution after the flies have laid their eggs. If cabbage maggot has been a problem in the past for you, cover transplants or direct-seeded crucifers with floating row cover. The cover acts as a barrier, preventing flies from reaching plants to lay eggs. To monitor for adult flies, use yellow sticky traps or a yellow flat water-pan trap placed on the ground in the field. These can also be used to detect onset of flight, intensity of the population, and when the flight declines. Pan traps can be made from any sturdy plastic dish (e.g. 9" dog dish) painted with Federal Safety Yellow, with a few holes drilled near the top to allow drainage after heavy rains. Fill with water and add a drop of soap to break the surface tension. Flies are attracted to the yellow color and to the moisture, and can be counted in the bottom of the trap. Other insects such as larger flies, wasps, striped cucumber beetles, and 12-spotted ladybeetles also come to the trap. Yellow sticky traps can also be used - these are placed vertically on stakes, near the soil. Check traps twice weekly.

Crucifer flea beetles are also active now. Their shot-hole feeding damage can set seedlings back if it is severe enough. If damage is light, seedlings usually outgrow the damage. Row covers offer excellent protection. Rotenone does kill the beetles, but since they move into crops frequently from other sites frequent spraying is necessary. However, rotenone has great detrimental effects to beneficials and health risks and I recommend avoiding frequent use.

European corn borer flight will begin within soon. If you want to detect the onset of the first flight, now is the time to get ECB traps set up! Use two Heliothis ScentryT traps, one baited with the lure for the Z (Iowa, I) strain and one for the E (New York, II) strain. Both strains are present throughout New England. Hang lures in the center of the lower opening. Place in weedy borders near early corn, with the base of the trap close to the top of the weed canopy. Place traps at least 50 feet apart to prevent cross-contamination of the pheromone plume that attracts the male moths.

Sources of traps and other IPM supplies include:

Where trade names or commercial products are used, no company or product endorsement is implied or intended. Always read the label before using any pesticide. The label is the legal document for product use. Disregard any information in this newsletter if it is in conflict with the label.

Frost was the big event last week. In Greene, Maine we had 4 frosts in a row, the first being in the mid 20s. Strawberry buds, flowers and fruit can be damaged by low temperatures. Buds are the least sensitive, but can be damaged when temperatures get into the twenties. Last week, even buds in the crown were damaged. The early flowers are now opening. Flowers that have been killed by the cold have a dark brown center rather than the normal yellow. These will not produce fruit.

Flowers are the most sensitive and with strawberry fields in Maine approaching full bloom, and with a full moon scheduled for the end of May, frost protection should be on all grower’s minds. Overhead irrigation or row covers are used for frost protection. For a complete guide to frost protection see the NRAES Strawberry Production Guide (from Cooperative Extension), or get in touch with me and I will copy that section for you.

Tarnished Plant Bug - TPB are being found in low numbers. We found the first TPB nymph yesterday. Be prepared to begin sampling for them when you get to 10% bloom. TPB nymphs are monitored by shaking flower trusses over a white saucer or sheet of paper and counting the number of nymphs that fall out. The action threshold for TPB nymphs is and average of 0.25 nymphs per flower cluster or greater than 4 infested clus-ters out of 30 sampled. The latter threshold allows you to simply note presence or absence of TPB nymphs in a cluster rather than counting them. Nymphs hatch within the 7 - 10 days of significant adult activity. (Be sure not to confuse TPB nymphs with green aphids. They look similar.) There is no truly effective organic control for TPB. The most important practice is to not mow any fields, especially clover or alfalfa, while the berries are in bloom. This would drive the TPB into the strawberry field.

Two-spotted spider mites - TSSM are being found in low numbers. TSSM predators, a predatory mite, have been found in my field in high numbers. Supplemental releases of these predators, Amblyseius fallacis, are recommended if TSSM are found without a high number of resident A. fallacis.

Strawberry Bud Weevil or Clipper - Early signs of clipper damage have been seen in the first opened flowers ( shot holes in the petals due to feeding). The real damage is the result of the beetle clipping the bud after it lays an egg. Scout field edges (especially near trees, hedgerows and stone walls), for clipped buds. There is no effective organic control for the clipper. Crop rotation is essential. If you note more than 10% damage this year it is probably time to move to a new field. Plow the old field deep right after the picking season to kill the pupating pest. On a small scale, the clipped buds should be collected and destroyed to prevent hatching of the eggs. Collect the clipped buds on a daily bases throughout the flowering period.

As mentioned in the beginning of this message, summer raspberries are at early pre-bloom, depending on variety and location. Growers should be scouting for cane borer adults by visually inspecting canes for live adults or puncture wounds, tarnished plant bug adults using visual inspections or white sticky traps, and two-spotted spider mites by looking at the under-side of the leaves in the lower 1/3 of the canes. See below for more information on cane borers.

Cane Borers - Raspberries are attacked by two types of cane borers. The raspberry cane borer is a ½" long, slender black beetle with an orange band just below the head and has long antennae. The female beetles girdle the tips of young raspberry canes by chewing two rings, about a half inch apart, around the stems about 3 to 6" below the top. An egg is inserted into the cane between the two girdled rings. When the larvae, or grubs, emerge, they feed inside the cane, tunneling downward, and eventually destroying the cane. Soon after the cane tips are girdled, they wilt, blacken, and may fall off.

As soon as the wilted tips are noticed, they should be cut off, several inches be-low the lowest girdle mark. Remove the infested tips from the field and destroy them. Also eliminate any wild brambles near the field which may be harboring this pest.

The red necked cane borer is ¼" long, slender, black with a "coppery" neck. Unlike the raspberry cane borer, it has short antennae. The red necked cane borer also causes a different sort of damage. The females insert an egg into young canes, usually within 10" of the base of the cane. They do not girdle the cane, but the presence of the egg, and later the grub, causes a swelling in the cane which can vary in length from ½" to nearly 3". These canes become weakened and may break off. Remove all canes which show the swelling and destroy them, and eliminate any wild brambles nearby which act as hosts for this pest. Regular removal of the infected canes and elimination of wild brambles often provides adequate control.

(About the author: Eric is MOFGA’s "extension agent" and can be reached at the MOFGA office to answer your questions about farming and gardening. Link to MOFGA Contact Page, or email Eric directly.)