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DAMPING-OFF

Last time I discussed damping-off of seedlings. This week I received a call about peas dying just after or just before germinating and I thought I better say that damping off can occur in the field too. This time of year the problem is with peas.

The disease is caused by several different species of Pythium, which is a common soil inhabitant that persists in soil in root debris as spores. The species have a wide host range of crops and weeds and so crop rotation will do little to avoid the problem.

During or just after germination the pea seedling begins to show symptoms. The symptoms may be as simple as yellowing and stunting because sometimes only the root tips are infected and this root pruning interrupts growth. Sometimes a soft rot of the stem kills the plant. Sometimes you just don't see any pea germinate.

High soil moisture and warm soil temperatures (warmer than optimum for pea growth, i.e., 65-75) favors Pythium. You can't control the weather but you can choose when you plant your peas. If the soil is very wet and warm weather is forecast it may make sense to delay planting a few days for the soil to dry a bit.

There are resistant varieties. The resistant gene is tied to some visual characteristics of the seed. Wrinkled seeds are more severely affected than round seeds. Also, some biological seed treatments such as Rootshield may help.

SEEDCORN MAGGOT

Peas, beans, corn, potato sprouts and even cucurbits in the greenhouse are attacked by the larvae of this fly. They are yellow-white maggots about a quarter of an inch long and sharply pointed at the head end. The symptom is usually that you see no germination, and when you dig around you may find nothing left or may find the maggots burrowing into the seed. Sometimes the seed germinates but only a weak or partially eaten plant is seen. The injury is most likely to occur in cold wet seasons where the germination is slow, and also in soil high in organic matter.

The attack is early in the spring because the critter spends the winter as pupae in the soil or maybe free maggots in manure or unfinished compost. The adult is a grayish brown fly only about a third of an inch long. It emerges in early spring and deposits eggs in rich soil, compost piles or near seeds and seedlings. Exposed peat or potting soil mix of transplants can also serve as attractive sites for females looking for a place to lay eggs. There are a few generations each season.

The best method of dealing with this critter is to do everything you can to encourage quick germination and rapid growth. In the cold, wet soils the seeds are just sitting ducks. Shallow planting helps when conditions are poor. Best yet, wait for things to warm up and dry out.

FLEA BEETLES IN BRASSICAS

Flea beetles are already feeding on early spring plantings of brassica crops in southern Maine. Numbers are likely to rise in coming weeks as beetles move out of field borders where they spent the winter. Crucifer and striped flea beetles feed on Brassica crops as well as weeds that are in the same family, such as yellow rocket or wild mustard. [Different species of flea beetles feed on the tomato family of crops. This is good to know when planning rotations.] The crucifer flea beetle (Phyllotreta cruciferae) is uniformly black and shiny, about 2 mm in length, while the striped flea beetle (Phyllotreta striolata) has two yellow stripes on its back. Flea beetle adults feed on leaves and stems, resulting in numerous small holes, or ‘shot-holes’. Eggs are laid in the soil starting in late May, and beetle larvae feed on roots. The non-waxy greens (arugula, bok choi, tatsoi, mustard, Chinese cabbage, komatsuna) are preferred to the waxy cabbage, kale and collard types of brassicas. In brassica greens, beetles feed on the whole surface of the leaf, and will continue feeding from the seedling stage until harvest. The crop quickly become unmarketable. Waxy crops are most susceptible at the cotyledon and seedling stage and feeding is more limited to leaf margins on older plants. Usually the crop outgrows the pest. Occasionally in tender greens such as arugula, tarnished plant bug feeding may be confused with flea beetle feeding. In addition to the shot holes from flea beetles, there may also distorted leaves that are typical of TPB feeding, which injures leaf tissue when leaves first emerge.

To reduce and delay flea beetle invasion of spring crops, move them as far away from the fields that were used for fall Brassica crops as possible. Beetles overwinter in field borders near last year’s crop. Planting close by ensures a high population in the spring. One of the best ways to protect Brassica crops from flea beetles is to place a floating row cover over the bed or row. It is critical to seal the edges immediately after seeding, because Brassica seeds germinate quickly and beetles rapidly find the cotyledons. Flea beetles can fit through extremely tiny cracks. Edges of the cover must be sealed on all sides using soil, black plastic bags filled with soil, or some other method.

Spinosad (Entrust is organic formulation) is proving to be effective in suppressing flea beetles and reducing damage. Pyrethrum (Pyganic EC 5) showed poor to moderate efficacy in trials, and has a short residual period. But, some growers have reported a good knockdown with this product. You can spray the Pyganic right through the floating row covers and knock down any flea beetles that may have gotten inside.

(modified from 2006 Mass. Veg. Notes by Ruth Hazzard)

OIL SPRAYS FOR MITES ON APPLE
(modified from Alan Eaton's UNH- IPM Newsletter)

Years ago, “dormant oil” was applied to smother scale insects and eggs of European red mite on apples. Eventuˇally, more highly refined oils were used, and it was discovered that a more effective timing was after buds had opened. The oils didn’t harm foliage when used properly. We continue this practice today, but the misnomer “dormant oil” doesn’t apply to the way we now recommend it on fruit trees.

The most effective time to apply what we now call “superior oil” or “spray oil” to control European red mite is at tight cluster stage. If San Jose scale is the target, then half-inch green stage is better. But we also have to have proper weather conditions to use this, without injury. We’d prefer to have temperatures remain above the 30’s for 24 hours after spraying. Even temperatures as high as 38 or 39F have sometimes resulted in some foliar injury. Of course, it can’t be windy either, or you won’t get proper coverage. In order to work well, you need thorough coverage, which means slow tractor speed, calibration, and high gallonage. When all these factors align, you can get 98 to 99% kill of the ERM eggs on the twigs. That’s what we’re aiming for.

For orchards with large acreage, there often isn’t enough time to get all covered if you wait until TC stage to beˇgin. When weather conditions are right and buds have reached half-inch-green, experienced growers go ahead.

With the price of petroleum as high as it is now, spraying oil might be an option that some growers skip this year. The fuel & spray material could be pricey. If you are thinking in this direction, think about mites. You’re more likely to have a mite problem if you don’t apply oil early for ERM eggs. With the mild temperatures we had this winter, I expect mites (and scales) have survived very well.

ASPARAGUS BEETLES
[Modified from the article by Ruth Hazzard, UMass Vegetable notes, May 1, 2008]

Common asparagus beetles will be active in asparagus fields shortly. The spotted asparagus beetle tends to become active somewhat later in the spring. These two beetles are closely related and have similar life cycles but it is the common asparagus beetle that is most damaging to the cut spears.

Common asparagus beetle (Crioceris asparigi) is blue-black, shiny, smooth and about 6 to 9 mm (1/4 inch) long, with three large yellow, squarish spots with red margins along each wing cover. (see photo). Eggs are black, laid standing on end in rows along the spears, and hatch in 3-8 days. Larvae are wrinkled, plump, hump-backed, and dull gray with black head and legs. They grow up to 1/3 inch. These larvae feed in spears and in fern. Eggs and larval damage makes spears unmarketable. Larval feeding damage in the ferns can cause sever defoliation and weaken the stand. When full grown, larvae drop to the soil and pupate underground. New adults emerge in July, feed in ferns, and by September are looking for overwintering sites.

Spotted asparagus beetle (Crioceris duodecimpunctata) is reddish orange or tan, with six black spots on each wing cover (hence its other name, 12-spotted asparagus beetle). Eggs are greenish, glued singly on their sides to leaves. Eggs are laid on fronds, not on spears. Larvae are similar to those described above, but are orange colored, and feed almost entirely inside the berries so they affect seed production but do not hurt the plants.

Winter habitat: Both species spend the winter as adult beetles either in field borders or within the asparagus field. Sheltered sites such as under bark or in the stems of old plants are preferred. Some burrow into the soil.

Life cycle: Beetles feed as soon as they become active, and begin laying eggs after several days of feeding. Eggs hatch in 3 to 8 days depending on temperature. Larvae feed for 10 to 14 days, molt four times, then crawl into the soil to form chambers in which they spin cocoons and pupate. After 5 to 10 days, new adults emerge. There are probably two generations in this part of New England.

Scouting: At this time in the season, look for adult beetles, for feeding damage and for eggs laid on spears. Michigan State recommends a treatment threshold of 5-10% of the plants infested or 1-2% of the spears with eggs or damage.

Cultural and biological controls. This time of year you can greatly reduce the population by harvesting ALL of the spears every day. Pick the field clean to reduce the number of stems where eggs will survive long enough to hatch and grow up into summer-generation beetles. If you harvest ALL of the spears right to the ground during the harvest period you will starve many of the beetles and fewer will make it to the time you stop harvesting and let the fronds grow. In the fall remove all of the crop residue and other refuse nearby that may provide shelter for adults over winter, by disking lightly or burn crop stalks and fronds.. Maintaining a clean environment in the fall will force beetles to seek shelter outside the field or burrow in the soil, where many predators reside.

There are several beneficial insects that attack the asparagus beetle, including a tiny parasitic wasp (Tetrastichus asparagi) that attacks the egg stage. It kills eggs by feeding on them and by laying its own eggs, which hatch and grow inside the beetle eggs. Providing a nearby nectar source such as umbelliferous flowers for the wasps may increase their chances of survival, but may not be sufficient to prevent economic damage.

Chemcial control. Entrust may be used on fronds after harvest, but asparagus is not on the EPA Entrust label for treating spears. Treat ferns if 50 to 75% are infested. Organic options on spears include Surround WP as a repellent, Pyganic EC5.0, or products containing capsaicin.

References: Handbook of Vegetable Pests by John Capinera; 2008-2009 New England Vegetable Management Guide; Eric Sideman, MOFGA; Brian Caldwell, Cornell Universtiy

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