Eric Sideman's Pest Report
July 12, 2000
I begin to believe it is summer when the corn ear worm arrives. Even with the temperature and wind outside more like September than July this is a sign it is the warm season. But times they are a changing. The earworm (and the potato leaf hopper) are here early this year. There is speculation that these pests have over wintered way north of their normal winter grounds and that is why they got here ahead of schedule. Is there any more doubt about global warming?
ALERT!!!
Reports from our farm inspectors is that there is damage from the leaf hopper in beans, strawberries and potatoes (curled leaves, yellowing at the edges). I have been noting this pest in the last two pest reports and if you have followed the advice and sprayed with Pyrenone or Pyrenyl or an equivalent you should not be seeing damage now. If you did nothing about it and you have a big infestation you will likely loose the crop. The yellow edges will turn brown and potatoes will go down by the first week of August. Beans will be dwarfed and produce little. Go out now and see how big your population is. Brush the plants to see if adults fly off and watch one land. The adult is light green and wedge shaped and tiny. The nymphs are just becoming active this week. Look on the underside of the leaves for very tiny, light green bugs similar to the adults but unable to fly. They run when disturbed...they can go sideways like a crab. If you see more than a couple when you look at about 10 leaves you better do something.
Corn
The corn is way behind last year but the very early crop (transplanted out or seeded under plastic) is now silking.When corn silk is green the plant is attractive to the corn earworm, which lay eggs on the silk and the worms crawl in and feed on the kernels. In addition, the European corn borer worms that hatch near the silk move in too.
Both worms are caterpillars so Bt (Dipel or Condor or the like) will kill them. But getting them to eat it is hard. We have been working with UMass on trials of a mixture of Bt and corn oil. We inject the mixture with a special applicator right into the silk channel. I suggest you do this too. Keep track of the flight of the pests by calling the corn hot line (933-4647) and when sprays are recommended because of large numbers in flight and you have green silking corn at that time, then inject the mixture when the silk just begins to wilt a bit. Applications in our trials consist of .5 ml per ear of a mixture of 1 quart of corn oil and 1 level tablespoon of Condor.
Corn Earworm
There were fewer captures of corn earworm moths in pheromone traps last week, but there are still enough to threaten any silking corn in some areas. Moths were caught in North Berwick, Cape Elizabeth, Gorham, Poland Spring, Auburn and Nobleboro. All silking corn should be protected from corn earworm when moths are caught in a field. Fields not yet in silk do not need to be protected from corn earworm. Recent cool nights may slow the activity of this pest, but more south to north moving storm fronts could quickly bring more moths into the region.
European corn borer
Pheromone trap catches of moths dropped off somewhat last week indicating that the first flight is winding down. There were still large numbers caught in cap Elizabeth, Corinth, Gorham and North Berwick. Check your field for damage. In addition to worms getting into the silk channel, the corn borer worms feed down in the whorl and eventually bore into the stalk. If you see pin holes in the leaves as they unfold out of the whorl you may want to spray Bt over the top of the crop (30% is the threshold for whorl stage feeding).
Fall Armyworm
The UMaine IPM team has caught one fall armyworm moth in their pheromone traps. However, they have found fall armyworm feeding damage in some fields last week. The FAW feeding leaves large ragged holes and lots of sawdust like excrement.This is an early arrival of this pest, and it poses another serious threat to sweet corn. When scouting, any fall armyworm feeding damage found is combined with any European corn borer damage found. If the combined damage exceeds 30% in whorl stage corn or 15% of corn at pretassel or beyond, a spray is recommended to control both pests. If more than 5 fall armyworm moths are caught in pheromone traps in a week a spray is recommended on any silking corn present.
Potatoes (Report from Jim Dwyer in the County) The potato crop continues to grow rapidly and looks excellent. The frequent showers of the past week have provided excellent growing conditions.
Shower activity has been extremely variable, but, the frequency of the showers and humid conditions has created ideal conditions for late blight development. While no late blight has been reported within the state of Maine, we strongly encourage all growers to be actively scouting for potato late blight. The more quickly that a potential outbreak is found, the more quickly it can be taken care of and the less potential for spread. Scouting is a valuable tool in risk management.
Aphids:
This week our yellow pan water traps have been catching low numbers of buckthorn and potato aphids. Trace numbers of non-winged potato and buckthorn aphids have been found within several potato fields.
European Corn Borer:
We are continuing to catch corn borer moths in our pheromone traps. Trap numbers are continuing to increase. Currently the highest trap counts are being found in Central Aroostook. The Iowa strain of ECB is the predominant strain being caught, with only trace numbers of the New York strain. Some egg laying is taking place, however, we feel that this is only minor activity at this time. We strongly encourage all growers, especially in Central and Southern Aroostook to carefully scout fields this coming week for ECB activity. The current modified growing degree-day accumulation is 725 as of July 6. We expect peak moth flight at approximately 900 modified growing degree-days and have been accumulating about 15 to 30 modified growing degree-days per day. The economic threshold for ECB is 1 egg mass per 15 plants scouted.
Colorado Potato Beetles:
A few fields within our scouting range are reporting some CPB activity. A variety of life stages can be found at this time, from egg mass to small larvae to large larvae through adults. Remember, the Bt for CPB only works on the small larvae. If you have a lot of large larvae you may have to spray with rotenone.
White mold
A grower reported problems with tomatoes and sent in a sample to the Pest Management Office for identification (a free service...491 College Ave, Orono, ME 04973).White mold is a disease that can persist in the soil for many years as resting bodies. It has a number of hosts that are common vegetables so rotation is complicated. In addition to tomatoes, carrots, beans, peppers and lettuce are hosts. The symptoms are white cottony growth over the bean or at the stem junction in peppers and tomatoes or all over the carrots, especially storage carrots and it causes lettuce drop.
Air circulation is important. Plants that stay wet during the day are at risk. Irrigate early in the morning to allow time to dry and give plenty of space between rows. Keep weeds under control. Remove any infected plants and destroy and cut out and destroy affected parts. Dusting with sulfur sometimes checks rapid spread.
(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.)