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Field and Forage Crops |
For Bollgard cotton fields(and that includes about 75 percent of the cotton in North Carolina), stink bugs, and to some degree plant bugs, will probably constitute our major insect concern for the remainder of the season.
As mentioned in the last two issues of the North Carolina Pest News, we have an unusual combination of exceptionally high stink levels and moderate plant bug levels coupled with very early boll setting in many areas of the state. This has set the stage for bug damage to bolls well before the onset of the major bollworm moth flights. In the last 4 days (July 6 to 9), we have had reports from three areas of the state with boll damage from bugs in the 10 to 20 percent range. With a high proportion of the bolls in the small susceptible stage for the next few weeks, a 10 percent internal boll damage threshold should be followed during this part of the season. That means that we have some fields that are already in need of insecticide treatment.
This bug problem should not be underestimated. A light trap in Duplin County earlier this week captured 177 stink bugs in two days. That is a lot of stink bugs. Within a week of the onset of blooming, all cotton fields should be monitored for bug damage. Remember that until our conventional cotton fields are treated for bollworms, these fields are just as vulnerable for stink bug and plant bug damage as are Bollgard fields.
The cutting open or squashing of 50 bolls in a field is suggested. Do not try to rate the amount of damage in a boll, only whether or not it is damaged on the inside with either a wart on the inner boll surface or stained lint. If the bug damage has occurred recently, the lint staining might be subtle. Count this anyway.
Plant bug feeding on large squares can result in blooms with some of the pollen anthers darkened and at times with slightly to moderately deformed, dimpled petals. These dirty blooms should also be monitored. More than 15 percent dirty blooms may indicate a treatable plant bug population.
Unfortunately, most of our plant bug and/or stink bug insecticides also can increase cotton aphid and bollworm survival. Materials such as Orthene, Bidrin, Lannate, Vydate and others fall into this category. The bollworm moth flights are approaching the southern part of the state, and aphid levels in general are also on the high side, so disruption of beneficial organisms is presently a concern, at least until the fungus become well established in the case of cotton aphids. The new chloronicotinoid insecticides such Centric are good against both plant bugs and cotton aphids, but leave more stink bugs behind than Bidrin, Orthene and the pyrethroid insecticides.
Once the major moth flight arrives and bollworm control becomes a factor, the color of adult stink bugs must also be noted. Pyrethroids, the insecticides of choice for bollworm control, also provide good control our two species of green stink bugs, but are only fair against brown stink bugs. For combinations of bollworms and brown stink bugs, a pyrethroid insecticide plus 4 ounces of Bidrin should provide effective control of both green and brown stink bugs. Orthene and Vydate at high rates also have shown activity against brown stink bugs in some tests.
In a test near Rocky Mount this week, we noted the appearance of the cotton aphid fungus, Neozygites fresenii, on a heavy population of aphids along with very high levels of aphid mummies and the associated wasps. This morning we received additional reports of the fungus from scattered areas of the state. Hopefully, the fungus is now on it's way to becoming more widespread and will significantly help with our cotton aphid problems over the coming weeks.
The major bollworm moth flight is expected to begin either this weekend or during the coming week in the southern part of the state. In the past, the earliest date that this flight has started (i.e., a significant jump in the two or three-day count of bollworm moth caught in a light trap) was July 9. Based on heat units and the advanced maturity of field corn in many areas of the state, we expect this flight to be early.
Peanut plant growth is good in most areas and insect pressure has been modest. A few fields are suffering from potato leafhopper damage which is the yellow V-shaped damage to leaflets. These insects come and go each year and we feel treatment is justified only when you see at least 25 percent of the leaflets with such damage. If you can tank mix, then you can save a few dollars of insecticide application cost. The impact of potato leafhoppers on yield is not fully understood, but we do know that heavy damage can reduce yield.
If you are concerned about rootworms in any of your fields, then your insecticide treatments should be applied. If you are still unsure about the decision to treat, refer to the rootworm advisory in the 2004 Peanut Production Guide. The rootworm advisory has been tested on hundreds of fields in North Carolina and Virginia and has been determined to provide solid guidance on making rootworm treatment decisions. Remember that applications of a rootworm insecticide also provides the added benefit of leafhopper control.
There is a lot of tomato spotted wilt virus appearing in peanuts. This is NOT due to a sudden increase in the virus in the field, but rather simply due to stress on the plants from hotter weather. This virus has been present in the plant since early in the season, but the symptoms simply did not appear until now. DO NOT apply a foliar insecticide thinking this will control thrips and reduce the spread of the virus; it will not help.
I have yet to receive any reports of spider mites but they are present in a few drier areas since they had a good start back in May. Watch for them now that we have some hot weather. It will soon be time to watch for worms as well. Over the past ten years we have saved a lot of insecticide sprays by scouting and not treating unless worms exceed 4 per row foot.
Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age or disability. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
Last modified on July 12, 2004 by Stephen J. Toth, Jr.
