Kudzu Bug Management and Control in Alabama Soybeans

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/.

Adults

Egg Mass

New Release Information on Kudzu Bug by Tim Reed

STATUS OF THE DISTRIBUTION OF KUDZU BUG IN ALABAMA

The kudzu bug has been “officially” reported to occur in 53 of Alabama’s 67 counties as of June 27. Last year in the first week of June this invasive species had been reported in 15 counties. It is quite likely that this insect is now present in all Alabama counties. Several counties have reported significant populations of kudzu bugs infesting soybeans during June in Alabama in 2013 and numerous fields have been sprayed. 

LIFE CYCLE AND HOSTS OF THE KUDZU BUG

The time required for the kudzu bug to develop from an egg to the adult stage is 6 to 8 weeks. The egg hatches in about 5 days. The kudzu bug has been found on many plants but presently the only host plants on which it is known to reproduce are kudzu, soybean and wisteria.

ECONOMIC THRESHOLDS FOR KUDZU BUG ON SOYBEAN

Thresholds for kudzu bugs infesting soybeans continue to evolve as more information is gained from research efforts. Southeastern entomologists are currently recommending that growers consider using the following thresholds when making kudzu bug treatment decisions: 5 bugs per seedling, until plants are one foot tall. Then, the threshold will change to 10 bugs per plant for plants from 1-2 feet tall. The established threshold of one nymph per sweep  should be used for plants above 2 feet tall. Plants should be sampled at least 50 feet from the edge of the field.

The reason for this is that the adults have an extended migration period (6-8 weeks) and colonize field edges first. If you sample the edges, chances are you will make a spray decision too soon before the migration is over.

WHICH CHEMICALS ARE EFFECTIVE IN CONTROLLING KUDZU BUG IN SOYBEANS

Multiple classes of insecticides have shown activity on kudzu bugs. Insecticide treatments containing bifenthrin, cyhalothrin, zetacypermethrin, carbaryl, or acephate provided greater than 80 percent control 2-5 days after treatment in insecticide efficacy trials conducted in Georgia and South Carolina. Insecticides do not prevent eggs from hatching. Growers actively treating kudzu bugs with broad spectrum insecticides should consider using a preventive application of Dimilin (2 oz/acre rate) at the R2/R3 growth stage for control of velvetbean caterpillars and green cloverworms in July, especially in central and south Alabama which historically have had higher populations of velvetbean caterpillars than north Alabama.

EFFECT OF PLANTING DATE ON KUDZU BUG POPULATIONS IN SOYBEANS

Studies in Georgia and South Carolina have shown that kudzu bug populations are higher on earlier planted soybeans than on later-planted beans.

Tim Reed, Extension Entomologist, Auburn University

Insect and Crop Update for the Week of June 23

After going weeks with light to moderate thrips pressure, damage was heavy on 4-7 leaf cotton in early June, especially in SW Alabama.

Cotton was growing rapidly but thrips damage on true leaves was showing heavy damage from about the 4^th to 7^th true leaf. (Peanuts also were taking heavy damage during this same period.)

The thrips window is over now and we need to shift our focus to spider mites, aphids and the plant bug complex which includes tarnished plant bugs, fleahoppers and an occasional clouded plant bug.

Mites are primarily found in the TN Valley region of North Alabama and some treatments were being applied last week.

I noticed the first aphids on April planted cotton in central Alabama last Friday (June 21).

Plant bug numbers (adults) were down last week but nymphs are beginning to appear in our earliest planted cotton (mid-April). I would suggest using a sweep net to sample adults for the next 2-3 weeks, depending on the age of the cotton. As we approach first bloom I would switch to a drop cloth and concentrate on the presence of immature plant bugs.

Also, field men should now be looking at pinhead square set. Fields surveyed on June 21 were setting about 90% of the fruit. However, some plants had up to 30% square loss at that point. I believe you will find that migrating adult tarnished plant bugs will seek out the earliest planted and most lush cotton fields. My thought is that this cotton provides the best shade from the 95 degree temperatures, and is the best host for plant bugs.

While looking for pinhead square set I noticed a number of white eggs, likely tobacco budworms. They would not be a concern now, but in the old days it would have created a real predicament. Spraying for plant bugs during a budworm moth flight would have been expensive and also put the grower on a treatment treadmill for the remainder of the season. Sometimes we forget how well we have it compared to the pre-Bollgard years.

On another insect – a few stink bugs are already present in cotton. Normally we do not worry about stink bugs until about the third week of bloom, when we have bolls that are 10-12 days old. However, when stink bugs are present at bloom they will attack thumb sized bolls as soon as the bloom tag sheds. Any feeding to bolls this size will cause the boll to abort. Therefore, fieldmen need to be alert for adult stink bugs in early bloom cotton as they monitor for plant bugs with a sweepnet. Stink bugs will not damage squares or blooms but will seek out these first small bolls.

Since some of our corn was planted later than desired, stink bugs will likely remain with that host until the post roasting ear stage when the kernels become hard. At that time we may have a large movement into other crops such as cotton, soybeans and peanuts.

One word about Kudzu bugs on soybeans. Numbers of adults are out of site on many of our April planted beans. In fact, adult numbers are beginning to decrease in some fields now but numerous immatures are present, which is the trigger we use to treat the field. Fieldmen who have not experienced this insect may overlook these immatures when they are small. They will be a clear to greenish color and very small after hatching.

Kudzu Bugs Infesting Soybeans

Kudzu bugs (adults and immatures) infesting April planted soybeans on Auburn University research farm, Auburn, AL.

Immatures

 

Immatures

Adults

Adults

Insect Update on Cotton and Soybeans

As of 8:45 am Monday, June 10, all is quiet on the insect front. Rainfall during the past week has given cotton a growth spurt. Youngest cotton is 3 to 5 true leaves and overall has little thrips injury. Older cotton is at the 5 to 9 true leaf stage. Many fields are between the thrips injury stage and the stage where we begin to focus on plant bugs. This window is about 7 to 10 days long. Mid April planted cotton already has 2-3 pinhead or larger squares and should be scouted for adult plant bugs. No aphids or spider mites have been reported.

We will be conducting scouting schools in Autaugaville (central AL) and Headland (Wiregrass area of SE AL) this week. In addition to cotton and soybean insects (Kudzu bugs) we will also have presentations on cotton disease and resistant weed management.

Kudzu bug adults are attacking early planted soybeans in the Prattville, Tallassee and Auburn areas. At present our treatment threshold is 5 adults per plant.

June 2013 Scouting Schools

2013 Alabama Scouting Shortcourses Announced

 

The following cotton scouting shortcourses will be conducted by Auburn Extension staff:

 

June 11: Autaugaville, Alabama, County Ag Center, Highway 14, for central and west Alabama

 

June 12: Headland, Alabama, Wiregrass Research and Extension Center, for southeast Alabama

 

June 18: Belle Mina, Alabama, Tennessee Valley Research and Extension Center, for northern Alabama

 

Cotton and soybean insects (description, recognition, life history and damage), seasonal occurrence, management recommendations and threshold levels will be discussed. Identification and scouting for cotton diseases will also be covered.

 

At the Headland and Belle Mina locations a special section will also focus on managing glyphosphate resistant weeds.

 

Commercial pesticide applicator recertification points will be awarded. Each program begins at 8:30 AM and will conclude after lunch with in-field visits.