Field experiments were conducted at Frederick, MD, in 1985 and 1986 to determine effects of weed-interference periods and insects on bell peppers. Weed-interference periods of approximately 40 and 60 d reduced both bell pepper fruit number and weight 10 and 50%, respectively. Bell pepper foliage weight was reduced 10 and 50% with approximately 20- and 50-day weed-interference periods. In 1985 and 1986, insect populations were low with an average of 10 and 3% of the pepper fruit infested, respectively. Most infested fruit was damaged by European corn borer. No significant differences in insect infestation of fruit as related to time of weed-interference periods were noted.

Field surveys were conducted to evaluate the prevalence of stalk-boring insects in giant ragweed in Indiana and Michigan soybean fields. Greenhouse studies were also conducted to determine whether stalk-boring insects had a negative impact on control of giant ragweed with glyphosate. In the June 2005 field surveys, 18 to 30% of all giant ragweed plants sampled contained stalk-boring insects or insect tunnels. Languriidae, Noctuidae, Pyralidae, and Tortricidae families were found most often at the time glyphosate was being applied to soybean fields to control giant ragweed. Cerambycidae and Curculionidae families were typically found later in the season after herbicide applications were completed. In the August field surveys in Indiana, 28 to 62% of the giant ragweed plants that showed evidence of stalk-boring insects were not controlled by POST herbicide applications suggesting that control was compromised by the presence of stalk-boring insects. In greenhouse studies, glyphosate efficacy on 15-cm-tall giant ragweed was enhanced by the presence of stalk-boring insects; however, glyphosate efficacy on 45-cm plants was reduced by the presence of stalk-boring insects. Overall, this research suggests that there is a possibility that stalk-boring insects could reduce glyphosate efficacy on giant ragweed.