Update for the First Week of July

The Alabama cotton crop is growing rapidly resulting from abundant rainfall from multiple thunderstorms that have occurred during the last 10-14 days.

Insect wise things have been rather quiet on cotton but not the case with soybeans which I will discuss later.

Tarnished plant bug numbers have not increased as rapidly as expected in fields that I have observed. An occasional adult and or nymph can be found, depending on the age of the cotton. Migrating adults went to the earlier planted cotton first and have had time to now produce offspring. Cotton planted on April 10 is now blooming in Autauga County, Alabama.

To my surprise, I’m finding as many adult southern green stink bugs as I am adult plant bugs. We need to begin watching stink bugs in early bloom cotton. As I have stated before, these stink bugs will feed on thumb size bolls as soon as the dried bloom sheds. A huge stink bug population is waiting in corn. These adults will migrate to cotton, soybeans and peanuts as corn begins to dry down. This may be the largest population in corn that I have ever observed. There seems to be mating pairs in every corn plant at our research farms in Shorter and Prattville, Alabama this week. Most are the southern green species with an occasional brown in the mix. That will be to our advantage in a few weeks since the pyrethroid chemistry does a nice job controlling the green species.

The other insect that is building on cotton is aphids. They are clumped in terminals on occasional plants in numerous fields at present. These clumps will spread field wide before natural diseases wipe out the population. I would project that aphid population decline will not occur until around July 20.

The most intense insect pressure at present is Kudzu bug populations on soybeans in select fields throughout the state. Ten to 50 adults and over 200 immatures per plant can be found in many April planted beans. More adult Kudzu bugs are moving into beans from Kudzu daily. Beans will have to be scouted weekly for the remainder of this and future seasons. One to three sprays may be needed to protect beans this season. This will open the door to pod and foliage feeding caterpillars for the remainder of the season.

Information on the management and control of the Kudzu bug in soybeans has been posted in blog entries previous to this one and also on the Alabama Crops website (alabamacrops.com).

Kudzu Bug Q&A

by Xing Ping Hu, Extension Entomologist, Auburn University

What is a Kudzu bug?
The Kudzu bug is a small yellowish green lady-beetle-like insect. However, they are not a beetle, but a true stink bug with sucking mouths that sip the juice from plants.

They like to aggregate in clusters and release a very strong, foul odor that you can smell several feet away.

Kudzu bugs are also called lablab bugs, bean bugs, globular stink bugs, and bean plataspids.

Are they a new pest and where did they come from?
Yes, the Kudzu bug is a new pest for us in the United States. Many new people are being introduced to it every day. We will all have to learn the best ways to deal with it.

The Kudzu bug is native to Asia. Genetic markers indicate this bug was likely introduced from Japan.

When did they get here and how widely spread are they now?
It was first reported in Georgia in 2009 and spread to Alabama in October 2010. Since then, it has been spreading like wildfire. By the end of June, it has been confirmed in more than 430 counties across 9 Southern Region States. They are in all but 53 counties in Alabama right now.

How do they spread so rapidly?
Many factors aid in their fast dispersal:

• Hitchhiking on vehicles, airplanes, shipments of products and equipment, and even humans
• They are strong flyers themselves, capable of flying at least a couple of miles
• They are attracted to white and lightly-colored surfaces
• Propensity to migrate
• Diverse and flexible life history and rapid population growth rate
• Availability of primary hosts – kudzu plants and soybean crops
• Most interestingly, the new finding in my lab shows a majority of the adult females become fertilized before overwintering. A single pregnant female can lay egg masses in a new location without the presence of male.

What plants do they infest?
Kudzu bugs are leguminous plant feeders. Their primary host is kudzu plants; that is how they got their name. Of the other leguminous crops, they prefer soybeans to vegetable beans and wisteria vine.

However, they must feed on kudzu or soybeans to be able to reproduce. It is common to see them aggregate and feed on non-legume plants in early spring and late fall when leguminous plants are not available.

If they have been in AL since 2010, why the sudden population outbreak in soybean crops this year?
During the first year of invasion, the population was basically limited to kudzu patches. However, because of the exponential growth, overcrowding populations started to move into soybean fields in 2012 and reached peak outbreak this year.

What is the pest status of kudzu bugs?
They were first considered a nuisance pest in residential areas, but are posing much greater threat than previously thought. In Asian countries, it is a serious pest of soybean and vegetable beans. Here in the United States, besides yield loss of soybeans, it poses threats to international trade of agricultural products to Central America, and is an urban nuisance.

What damages do they cause in soybean crops?
They are slow feeders, sucking plant juice and gradually drawing down a plant’s vigor. They do not eat holes in leaves and do not take bites from pods or seed.

When do kudzu bugs move onto soybean plants and how long they stay in soybean field?
It depends on whether you have early, middle, or later soybean crops and the climate. In 2013, we observed adults of an overwinter generation move to lay egg masses on early-planted soybean crops when they are about 1 ft tall. Nymphs appeared in late May and by the middle of June, nymph population had peaked across the entire soybean field. This was also the optimal time for control treatment.

You will see Kudzu bugs in the field until the soybean plants become unsuitable (not enough juice). Last year’s research showed that Kudzu bug population was greater in early-planted soybeans rather than later-planted soybeans. We are monitoring Kudzu bug population dynamics this year.

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