MOFGA Pest Report 2005
9 May/h2>
(View List Of All 2005 Pest Reports)
It is still wet out there. In some fields, it is very wet and soil preparation and planting are being delayed. Remember, your short term gain from going into a field when it is too wet will be well out weighed by the long term loss of soil quality. When soil is too wet to work and it is worked anyway it becomes compacted and soil structure is destroyed. A simple test to see if your fields are ready to plow or till is to take a handful of soil and squeeze it into a ball. Then take your thumb and press against the ball. If it crumbles, the soil is ok to work. If your thumb sinks into a clay-like mass then stay off of it until it dries enough.
Cutworms
In last week's piece on cutworms I forgot to mention what may be a very good tool for managing cutworms in your fields. Some species of nematodes (microscopic, or nearly so, round worms) are beneficial and attack insects, and some of these live in soil and attack soil dwelling insects, such as cutworms. These parasitic nematodes enter the pest and release bacteria which actually feeds on the pest. The nematodes reproduce in the soil and, if the conditions are good for them, large populations of the nematodes can build up and these will hold the number of cutworms down.
You have to use the correct species of nematode. Heterorhabditis bacteriophora [Hb] and Steinernema carpocapsae [Sc] are often used in combination because they live and attack insects in different levels of the soil. This works well for cutworms that move up and down. The nematodes are shipped to you on a sponge. You mix them into water and apply to the soil. Follow the instructions that come with them carefully. The nematodes will not live if conditions are not favorable for them, especially if the soil is too dry.
Here are a few well known suppliers of parasitic nematodes. Call them and tell them which pest you want to control and about your farm. Then compare prices.
ARBICO- 800 827 2847
Green Spot- 603 942 8925
Hydro-Gardens-800 634 6362
IPM Labs- 315 497 2063
Johnny's Selected Seeds- 207 861 3900
North Country Organics- 802 222 4277
Lily Leaf Beetle
This is a relatively new pest in Maine that feeds on lily foliage, chewing large ragged holes in the leaves and often consuming all of the foliage except for the stems. This, of course, will lead to the death of the plant. Most of the feeding is done in June and may go into August, but I have already heard a report of the pest.
The lily leaf beetle overwinters in plant debris or soil as an adult which emerges in the spring. The females lay reddish orange eggs in a line on the undersides of lily leaves. The larvae feed for a few weeks and then pupate in the soil, later to emerge as a new generation. There are 2-3 generations per year in Maine.
In small plantings the best control is hand picking the adults and larvae. Inspect the leaves carefully and pinch off any eggs you can find. Neem products and insecticidal soap should give acceptable control if hand picking is not feasible.
Powdery Mildew on Hoophouse Tomatoes
(adapted from CT Ag Experiment Station by Vern Grubinger)
The pathogen Oidium lycopersicum is relatively new to the Northeast and is not the same one that causes other powdery mildews that have been around quite a while. This year it has already been a serious problem in at least one greenhouse operation I‚m aware of.
Symptoms first appear as light green to bright yellow spots on the upper surface of the leaf. The spots become more noticeable as they develop the typical white, powdery appearance. Powdery mildew of tomato is more aggressive than other mildews and once leaves are infected, they quickly turn brown and shrivel on the plant. The fungus spreads easily as abundant powdery spores are carried by air currents or production activities. Conditions that favor the disease are common in the greenhouse: high humidity and warm temperature, but unlike most other fungal diseases, water on leaf surfaces is not necessary for infection. Other hosts include rosemary, pepper, eggplant, and many bedding plant and weed hosts.
To prevent this disease do not grow bedding plants or ornamentals in the tomato house. Use adequate spacing between tomato plants to allow good air circulation. Maintain relative humidity below 90% using well-timed heating and venting. Scout regularly to identify outbreaks before they can spread. Diseased tissue should be removed as soon as it‚s detected by placing it in a plastic bag ˆ do not carry infected material through the house. Production areas should be thoroughly cleaned and all plant debris removed between crop cycles. Control weeds in and around the greenhouse. If you have this problem, avoid susceptible cultivars in the near future, including Caruso, Match, or Trust.
To be effective, organic sprays should be applied as soon as symptoms are first observed since early control is critical. Be sure to get complete leaf coverage. Among the compounds registered for use in most states are bicarbonates, cupric hydroxide, sulfur, and Ampelomyces quisqualis (a biocontrol).
Cabbage Maggot
The cabbage maggot is the larvae of a fly that tunnels through or eats the roots off of plants in the cabbage family such as turnips, radish, cabbage, broccoli and cauliflower. In root crops you may find the tunnels or the maggot. In crops such as broccoli or cauliflower your first sign of problems is wilting of the plant on sunny days and then later the plants die. If you pull one up you will see the reason it is wilting is the roots are gone. You may still find the little white maggots feeding.
Cabbage maggot flies resemble houseflies but are only about half as long, 1/4 inch (6 mm). They are dark gray with black stripes along the body. Adults emerge in late April and May. They lay eggs at the base of the host plant and when the eggs hatch the larvae crawl down and begin feeding. There are 3-4 generations per year.
Because of the variation in time of adult emergence in the spring, and the variation in length of developmental stages, it is possible for maggots to be present much of the growing season. However, high temperatures and disease suppress populations in July and August. The major damage from this pest is found in the early plantings of broccoli, cauliflower and cabbage. Then again in the end of the season since the cooler temperatures of September and October favor development. At that time, the maggots damage fall-maturing plants such as rutabagas, turnips.
Organic management for the cabbage maggot:
It is important to remove roots, root crops and other host plants, and destroy them in the fall. Destroying wild host plants, especially the mustards at any time will help.
Fall tillage may also expose over-wintering pupae to predators and drying. Use resistant or maggot-tolerant plant varieties if available and if cabbage maggots have been a problem in previous years. Good soil fertility will help damaged plants overcome injury.
On a small scale, there are ways to prevent maggots from getting to the root zone. A small piece of plastic, slit to the middle, wrapped around the plant stem and overlapped, can be taped or covered with soil. Another method uses 2 pieces of plastic about 12 inches square, pulled together around the plant from opposite sides and held down with soil. On a larger scale, floating row covers placed over the crops at planting will exclude the fly. This is probably only cost effective and feasible for the early season plantings of the brassica family. I cover all of my brassicas in the spring and keep the covers on until the flowers drop from the forsythias.
A good website for cabbage maggot info is:
http://oregonstate.edu/dept/hort/faculty/stone/magnethomepage.html
Strawberry Rootworm
The damage from the strawberry rootworm is twofold. The adult damages the leaves and the larvae eat the roots. Adults are out in the strawberry fields right now and if you are seeing a lot now you will probably see them again after renovation of the beds in July.
Strawberry leaves attacked by strawberry rootworm beetles are riddled with small holes. Some leaf damage occurs in May, but most occurs in August. Heavy infestations can reduce plant growth or kill plants. As foliage grows back after renovation, keep an eye out for feeding of strawberry rootworm (Paria fragariae). Although feeding of the adults of the strawberry rootworm is more obvious, root-feeding by the larvae is more damaging to strawberry production, and that is what will happen between now and July.
Adult strawberry rootworms are brown to black or copper-colored, shiny, oval-shaped beetles with four blotches on the shell-like wing covers. They are 1/8 inch long. The larvae are grubs that are 1/8 inch long, creamy white, with three pairs of legs. Adult strawberry rootworms overwinter in mulch and soil crevices, and become active in May and June. Adults feed primarily at night and hide in soil or mulch during the day. They chew small holes in leaves, and females lay eggs on older leaves near the soil surface. Larvae burrow into the ground to feed on strawberry roots from late spring to early summer. New adults begin emerging in mid-summer, and these beetles feed on strawberry foliage through early fall. Scouting for the presence of adult beetles is best done after dark using a flashlight to examine plants. No threshold has been established for this insect, but a population of 10 to 20 beetles per square foot is considered high. As with all the root feeding insects, control of the root feeding stage is very difficult. Therefore, insecticide control measures for strawberry rootworm should be directed toward the adult stage. If feeding injury is observed in May or June, an insecticide spray at this time will reduce the number of egg laying females and, therefore, the number of grubs feeding during the summer. When the next generation of adults emerges in July or August, control measures may be needed again. I am searching for info about efficacy of some insecticides such as Pyganic. The only control that really works for organic growers is to rotate out of the field after one or two years of picking for two years.
(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.)