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Eric Sideman's Pest Report

August 6, 2001

NOTE: A premier mixed vegetable farm in eastern New York (near Saratoga Springs) is in a bit of trouble and needs workers. The husband of the the husband/wife team had a tractor accident and broke his leg. If you have an extra apprentice who may want to work with them it would really help them out. Even starting in September would help. Let me know and I will send details and contact info.

Crop Condition

As if you did not know it already, it is dry. Some places that missed all the showers back in July are in a severe drought condition. The dry weather can have very negative effects on plant growth even beyond the obvious. For example, pollination in corn is disrupted and you will end up with only partially filled out ears. If you can, get water to the crops before they wilt. Insect and disease pressure remains low around the state. Things can change very quickly if we get a good southern storm moving up the coast. Keep your eyes open if that every happens.

Corn

The corn pests remain in low numbers. European corn borer catches are relatively low with only a few locations being above threshold for spraying. Look for shot holes in leaves as the unfold from the whorl or holes in the side of ears. They will also enter through the silk channel, but with moth counts low I don't think a spray is called for at this time. Corn earworms were only active on Cape Elizabeth last week. The first fall armyworm moths were caught this week, but at low numbers and no spray is recommended yet. CEW and FAW will show up in big numbers if we get a southern storm. There has been no report of second generation common armyworm yet.

Beans

The Mexican bean beetle larvae are out now. Someone described them as a yellow cross of an insect and a porcupine. They will do great damage in high numbers. Crop rotation does a good job in keeping numbers down from year to year, but if you have a large population you may want to spray with rotenone. The larvae will become adults in a few weeks. Adults hibernate over winter in crop debris. Clean up and destroy or plow under bean debris at the end of the season and plant beans in a different field next year.

Potatoes

Jim Dwyer says that as of this writing, no potato late blight has been reported anywhere in the State of Maine. All growers should be scouting their fields for potato late blight. The earlier that late blight is found the better likelihood of controlling it with copper. Remember, good sanitation is the starting point of control as late blight overwinters in the old tubers. Aphid populations in untreated plots are starting to build. Some buckthorn and mostly potato aphids are being found at this time. Sporadic wingless green peach aphids are also being found in some fields. If populations get high, or you are raising seed potatoes and are real concerned about virus, then you better scout and spray pyrethrum if you need to.

POTATO LEAFHOPPERS:

Potato leafhoppers are now being found in the central and southern Maine. I strongly encourage all growers of potatoes and beans to be actively scouting fields for potato leafhoppers. Leafhoppers will be found on the underside of leaves. Both the larvae and adults will appear almost neon green and many times move sideways with a crab-like movement. The adults will fly when disturbed and land a short distance away. Symptoms include curling and yellowing of leaves. If you let them feed too long the plants will never recover. Hopper burn, or tip burn is what the later damage is called. The edges of the leaves yellow and then brown up and eventually the planting goes down. Rotenone does not work well. The concentrated pyrethrum products do a good job if you catch them early. Deer

ELECTRIC FENCE FOR DEER: ONE GROWER'S COST FIGURES (from UMASS Report)

(If you have deer problem and are considering fencing, call the USDA office and talk to them about their loan program- 622 8263)

Is it cost effective to put up two-strand electric fence for deer control?

Will it keep deer out? I recently talked with a grower in central Massachusetts whose pumpkins and squash have suffered serious deer damage in past years. For the second year he has installed electric fence in his fields and is very happy with the results. Recently he set up fence for a 4-acre field. Here are his costs:

  • $200 - solar charger
  • $30 - corner posts (5-foot T-post for strong corner support)
  • $30 -insulators
  • $70 -wire (17 gauge wire)
  • $120 -rods for supporting fence. He buys 3/8 inch solid round metal rods and has them cut to length, $1 each. Spaced 25-30 feet apart. Total materials cost: $450, or $112.50 per acre. Total labor to install: 2 workers, half day.
He places the strands at 18-20 inches and 48 inches. He baits it right away with peanut butter in heavy aluminum foil squeezed onto the wire, about 12-14 baits for four acres, placed on the sides near the woods where deer would enter the field. He finds that baiting once is enough, since deer learn to avoid the fence once they contact it, and he gets fence up before they start feeding in a field. His experience with this fence: deer do not cross it.

All parts will be reused next year except the wire, which he discards because it is lightweight and tangles easily.

How many pumpkins (made unmarketable because of one deer bite) does it take to recoup the investment of less than $150 per acre?

TOMATO (modified from UMASS report)

If night temperatures drop into the forties, tomato flavor may be affected. If cool nights < 50 F are expected, picking at the breaker stage and allowing fruit to ripen inside may result in better flavor. This does not seem a problem this week with record warm nights predicted, but August can be pretty cool up here in Maine.

As the season progresses, tomatoes tend to show more symptoms of bacterial and fungal diseases. It can be difficult to identify tomato diseases from field symptoms-but it is important, since management choices will be different depending on which disease is present. The following paragraphs describe symptoms of key diseases that are currently being found in tomato fields: Early blight, caused by the fungus Alternaria solani, is characterized by brown to brownish-black lesions on foliage which form distinctive concentric rings as they enlarge. These lesions may be surrounded by a yellow halo. The lesions tend to form on older leaves first and work their way up the plant to the newer growth. These symptoms eventually grow to cover the entire leaf and under favorable conditions may lead to defoliation, which will reduce yield. Tomato fruit can be infected as well; fruit lesions are dark brown and leathery, and may be covered by a velvety mass of black spores. Fruit lesions are at the stem end instead of the blossom end as is the case with blossom end rot. Plant stress increases severity, and adequate nitrogen and water can reduce it. Recent dry conditions, low humidity and cool nights mean low risk of early blight. Ten to fourteen day spray intervals with copper should be adequate. Good crop rotation and mulch to prevent splashing is the most important defense.

Septoria leaf spot, caused by the fungus Septoria lycopersici, develops under similar weather conditions as early blight; as a result, the diseases often appear together in the field. However, the symptoms are distinct. Symptoms from Septoria infection appear as numerous small tan spots surrounded by brown tissue; small black pepper-like fruiting bodies, called pycnidia, form in the center of each spot. Septoria spots are usually more rounded than spots caused by bacterial diseases.

Infected leaves will turn yellow, then brown, and eventually wither and fall off, also resulting in reduced yield. Fruit is not directly infected by the fungus.

Copper will work with septoria too. Remember that you are protecting healthy tissue when you use copper. As the plant grows, new tissue is exposed that will need protection. Spray before there is significant crop injury if you want good results.

Bacterial canker: typical symptoms on foliage are "scorching" of leaf margins-brown, crisp edges of the leaves, with a thin, yellow chlorotic band inside the burned tissue. This "secondary infection" is what we see most often. Fruit may have "bird's eye" spots, small raised scars with a tiny brown center surrounded by a white halo. Symptoms of systemic infections include stunting, wilting (especially one half of a compound leaf), development of open stem cankers and fruit lesions. Canker can be seed-borne. It will be carried over in non-rotated fields for at least one year.

Bacterial speck: Symptoms of speck are tiny black spots on leaves, which soon develop a yellow halo. Small black specks can also be seen on fruit. Leaves with a lot of spots usually turn yellow and fall off. This disease is seed born and when wet weather comes along, the disease can really get going. Splashing water from heavy rains will spread the disease easily. When the leaves are wet, bacterial speck is easily spread by tractors or people as well. If either of these bacterial diseases is present, applications of copper on a weekly schedule may reduce the spread of the disease. If possible, applications should be made with a boom sprayer, as an airblast sprayer can spread the bacteria to new locations in the field. If possible, harvest infected fields only when they are dry to avoid spreading the disease. No late blight has been reported in the region.

CUCURBITS (Modified from UMASS report)

There is a wide range in maturity for pumpkin and butternut -early, vigorous crops have some full sized fruit, while later crops are just beginning to flower. Early crops may still be setting fruit on the same vines. In general, fruit set in vine crops appears to be good. Hot days last week caused abortion of female flowers in some fields - these flowers never opened before aborting. Females further down the vine are fine and setting fruit or are ready to open in the next day or two. Septoria leaf spot is being found in butternut squash. Bacterial wilt is causing some plants or vines to drop. Some growers report that vigorous efforts to control cucumber beetle seems to have paid off, with less wilt evident.

Scout the field for squash bugs. Lots of eggs have been seen on farms around the state. The eggs are on the underside of the leaf and are a reddish copper color. If you have lots of egg masses you will have lots of squash bugs. Be ready. They will congregate on leaves now but later will move to fruit and create "warts" over the skin. Pyrethrum will kill them. Crop rotation and sanitation are important as they overwinter hibernating in debris.