Stephen J. Toth, Jr. and Thomas A. Melton, editors
Volume 17, Number 1, April 19, 2002

Field and Forage Crops

From: Jack S. Bacheler, Extension Entomologist

Unfortunately, the timing, abundance, and severity of our upcoming insect problems defy even a mid to late-April prediction. Overwintering pest and beneficial insect survival, the abundance and quality of nearby crop and weed hosts, cotton crop development, and most importantly, weather (both here and elsewhere) all will affect this year's insect levels. We must also contend annually with insect pests that undergo several generations before "playing their hand." This makes early predictions even more difficult. Some observations, however, are provided:

1. Thrips have been problematic the past few years, with 62 and 51 percent of our cotton acreage receiving a foliar application for thrips in 2000 and 2001, respectively. Do not overlook the possibility of a foliar application as early as the expanded cotyledon to first true leaf stage. With a seed treatment (Gaucho or Cruiser), a grower can almost count on the need for a foliar spray. With the high thrips levels that are all too common here, consider the upper end of the ranges of rates for foliar insecticide sprays.

2. Plant bugs will likely be kind to most producers in the pre-bloom period, but a possible headache in post-bloom Bollgard cotton, particularly in our counties located in the far-eastern part of the state. Weekly square retentions should define most potential problem fields up to about two weeks post bloom. Combination stink bug/plant bug crushing or cutting of quarter-sized bolls is probably best correlated with the need for insecticide treatment -- though also monitor dirty blooms and adult/nymph ratios.

3. Bollworms have seesawed up and down for the past 6 years. If the trend continues, watch for a tough year for bollworms. An early high moth flight at the Rowland black light trap (near the South Carolina border) seems to inevitably signal Bollworm City for points north. Counts from this trap and others can be found on line at the Cotton Insect Corner web page (http://www.run.to/cotton) beginning early July.

4. Other caterpillars, such as fall and beet armyworms, European corn borers and loopers have generally taken a hike in recent years. I hope this trend continues, though new insecticide products are now labeled to control armyworms and loopers far better than in the past.

5. Stink bugs, seemingly more of a problem since we passed the 50 percent B.t. (versus conventional) cotton mark in 2000, will probably be back for another banner year in 2002. Adequate sample sizes, a lot of interior boll examinations, and calculation of green versus brown stink bug adult ratios are a must in Bollgard fields. In 2001, a number of conventional cotton fields also took a lick (or puncture) -- to an average of 2 percent stink bug-damaged bolls.

With very few exceptions, cutworms are rarely a problem in conventionally-tilled cotton. In various forms of conservation tillage, such as stale seed beds, no-till or strip till, weed residue (especially if burned down less than 2.5 or three weeks of planting) can support damaging levels of cutworms which can then move onto the remaining green foliage -- cotton seedlings. In general, significant cutworm reductions to stands is more the exception than the rule in reduced tillage cotton. Scouting for cutworms and treatment based on a stand loss of about 10 percent along with live cutworms is recommended where possible, although the thoroughness of the scout, the size of the cutworms, the distribution of the damage and the density of the plant stand itself should be taken into consideration. Cutworm scouting is difficult, as these caterpillars invariably hide below the soil surface under clumps or within cracks during the day.

A history of cutworm damage in a conservation tillage cotton field, if known, may argue for a pre-planting or an at-planting insecticide treatment. Pyrethroid insecticides are very effective and inexpensive for cutworm control, although pyrethroid labels can be confusing with some labels suggesting low rates (Karate, Baythroid and Fury), while other labels suggest their full rate ranges (Asana and Decis) for cutworms. For an at-planting, in-furrow foliar approach, one quarter of the industry rate for bollworms (see the North Carolina Agricultural Chemical Manual) should provide more than enough activity for good cutworm control. I will discuss post-emergence cutworm control in a subsequent issue of the North Carolina Pest News.

An early-season thanks to our independent crop consultants and county agents, who supply the cotton project at North Carolina State University with most of its information about insecticide use on B.t. and conventional cotton, assist with applied research, advance scouting and threshold technology, relay pest status or outbreak situations, and ask difficult questions. Please help keep us informed during the current crop year.

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 22, 2002 by Stephen J. Toth, Jr.