 |
Field and Forage Crops |
The cereal leaf beetle is now actively infesting wheat fields across North Carolina and county Extension agents, growers, consultants and dealers are very interested in this insect. The cereal leaf beetle was late to emerge and move into small grain fields this season, presumably due to a slow accumulation of growth degrees (cool weather). Although fields are now being colonized, numbers are low. Steve Gibson, Extension agent in Cleveland County, and others have e-mailed or called in order to confirm this observation and question it's cause. My observations, and those of others, are mostly of low general populations but high egg plus larva counts in some fields or portions of fields. I believe that most beetles have emerged and moved to grain fields by now. I would expect low populations this season because of the small 2003 wheat crop (mainly in the Coastal Plain) and the excessively wet season last year. The cereal leaf beetle has one generation per year and this year's adults came from last year's crop. A very small crop likely produced proportionately small numbers of beetles. In addition, this insect pupates in the ground in late May/early June. Last year, this period was very wet in many areas and I suspect that pupating conditions were not favorable for high survival. Wet weather may have also reduced beetle numbers in the warm month hibernation (aestivation) period.
Our objective with cereal leaf beetle management, at this time, is to find above-threshold populations before larvae become large. Most leaf tissue is eaten by large larvae and this happens very rapidly. Growers usually suffer yield reduction unless high populations are found early. Consequently, the scouting targets are cereal leaf beetle eggs and small larvae (threshold equals 25 eggs and/or small larvae per 100 leaves). If above-threshold populations are found, Warrior or Mustang Max are recommended for control. According to data from Dr. Ames Herbert, Virginia Tech University, Warrior (2.56 ounces per acre) provided greater residual and is better suited for populations with high egg counts than is Mustang Max at lower rates (e.g., 2.24 ounces per acre); the high Mustang Max rate (e.g., ca 4 ounces per acre) should be used against very young cereal leaf beetle populations. However, threshold populations with few eggs could be successfully treated with the lower Mustang Max rates or Warrior.
The following is an excerpt from Steve Gibson's (Extension Agent, Cleveland County) newsletter: "The real surprise is the very, very low levels of cereal leaf beetles. Yesterday I made a near complete tour of Cleveland County and scouted 6 late planted fields. Four of the fields had only 10 percent of the tillers with eggs, the other two had 30 percent. Furthermore, I observed many eggs that obviously had been laid, but for some reason never developed into larvae. Also, the adults are seemingly much less numerous. Last year, ten days prior to today, I sent out a note that fields were typically at 70 percent of the tillers with eggs."
This report is consistent with reports from John Van Duyn, Extension Entomologist, Vernon James Research and Extension Center, Plymouth, and Kathy Kidd, North Carolina Department of Agriculture and Consumer Services. Last week we received a wheat sample from Robeson County with a few eggs just beginning to hatch. Many growers may escape a treatment or, at least, only need one good one. Speculation may include low numbers going into the winter, a long cool winter, or active beneficials. I guess we will never know, so enjoy it while you can.
The relatively warm and dry April is causing us to think more about the potential problems we will face this year in peanuts. My experience has shown that a warm, dry April is the primary contributing factor to spider mite outbreaks in July and August. Of course, if July and August are cool and wet, the outbreaks will not occur. However, if these months are normal or hotter and drier than normal, then we really need to watch for spider mites in 2004.
A month ago we felt that the conditions for tomato spotted wilt virus were not all that impressive for a major problem in peanut in 2004. However, the warm, dry weather has caused us to elevate our level of concern for tomato spotted wilt virus in peanuts this year. While our ability to predict still needs refinement, we know that the warm weather has caused thrips to start moving, transmitting virus and reproducing. If these weather patterns continue, then we could see rather significant movement into peanuts in May and a resulting higher level of virus. This major movement into peanuts in May did not occur in 2003 and we had less virus. A lot could change between now and then, but the trends indicate that the virus may be higher in peanuts this year than last.
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 April 26, 2004 by Stephen J. Toth, Jr.