Ron Smith, Extension Entomologist, Auburn University
The Kudzu bug has become a major economic pest of Alabama soybeans in certain fields throughout the state in recent weeks. Populations as high as 50 or more adult bugs per plant were observed in early June. Some of these fields now have 200 or more immature bugs per plant (late June). Calls are being received from growers and field men in recent days from all over the state.
Kudzu bugs are most highly attracted to early planted (April and early May) soybeans. Beans planted later, for example following wheat harvest, are much less attractive.
The primary question asked are when should soybeans be treated and what insecticide should be applied. The second part of the question is the easiest to answer. Most pyrethroid insecticides do a good job of controlling Kudzu bugs. Working thresholds have been previously established by entomologists in Georgia, North Carolina and South Carolina. For pre-flower vegetative beans a treatment threshold of five adults per plant is suggested. After flower, a threshold of one immature per sweep, with a sweep net, is recommended. As an alternative to sweep-net sampling, visual inspections of insect density lower in the canopy will suffice. If immature kudzu bugs are easily and repeatedly found on the leaf petioles and/or main stems, treatment is likely warranted. However, these threshold guides may be modified slightly based on the number of egg masses that are continuing to hatch.
Kudzu bugs have two generations per season on soybeans. Adults move from Kudzu to early planted soybeans in the spring, deposit egg masses and eventually die. The immatures then hatch and eventually become adults after about six weeks and begin to deposit eggs for the next generation.
A limited number of Kudzu bugs may appear in beans season long. The most efficient and economic use of insecticides occurs when an application is made when the majority of the population in each generation is in the immature stage. Some fields have already exceeded treatment threshold and will likely require two or more sprays during the 2013 season. Fields with lower populations may be able to wait until mid-July or later for a treatment. Only one application may be needed in these fields during the 2013 season.
Applications made when a high number of unhatched egg masses are present may have to be repeated within one to two weeks. Our goal should be to strategically time these insecticide applications for maximum effectiveness. Treating soybeans repeatedly at close intervals has not resulted in yield increases over fewer well timed applications. The key point is for growers and field men to focus on the peaks of immature Kudzu bugs as we move through the 2013 season.
There will be no way to economically prevent yield losses to Kudzu bugs and minimize inputs without monitoring or scouting soybeans weekly just as we have done in other row crops for decades. Kudzu bugs are not the end of the world for soybean production in Alabama but they do create a new day. Pictures of adult and immatures are available on Ron Smith’s blog http://alabama-insects.blogspot.com/. Basic Kudzu bug information can be found at http://www.clemson.edu/extension/Kudzubugs/index.html. Updates on the Kudzu bug status will be posted on the www.alabamacrops.com website. The Extension Soybean IPM guide has recommendations for Kudzu bugs on page six http://www.aces.edu/pubs/docs/I/IPM-0413/IPM-0413.pdf. Also, there is a podcast now available here http://agfax.com/2013/07/01/first-time-with-kudzu-bugs-listen-up/.