Stink Bugs Showing Up in Fields

Based on calls from consultants during the past seven days, most insect attention on cotton in Alabama has now shifted to the stink bug complex. This appears to be the appropriate thing to do since no other widespread destructive insect is being reported and a high number of stink bugs are being reported from all the major row crops. This began with wheat during the spring months. Stink bug numbers later shifted to corn. High numbers have been reported in recent weeks in peanuts, with increasing numbers being reported in both cotton and soybeans.

If we back up and review the situation since the end of the 2012 season, this is as expected. Stink bugs built high numbers on soybeans late last season resulting in a high level entering overwintering sites. This past winter was mild and we did not have the excessive high temperatures or extended drought this spring to limit a 2013 population build up.

This complex included both the brown and the southern green species. In the more southern counties within Alabama, the leaf footed bug is also in the mix. Leaf footed bug damage is identical to stink bug damage to cotton bolls. The important thing here is that, control wise, they are more like the brown stink bug. Phosphide insecticides do a much better job in controlling brown stink bugs and leaf footed bugs than do pyrethroids. Growers will need to keep this in mind as they select their chemical for treatment decisions. In Alabama, escape bollworms on Bollgard and Widestrike cotton varieties have not presented a big enough problem to select a pyrethroid over a phosphate for stink bug control. Field monitoring between July 20 and August 10 will determine if that trend holds true for the 2013 season.

In a few weeks, as we begin to make more stink bug control decisions in soybeans, we will have to work more with the pyrethroid chemistry to suppress the brown stink bugs in the complex. Research trials across the south point to bifenthrin as their superior pyrethroid for brown stink bugs in soybeans. We can improve the percent control by using the higher labeled rates.

Back to cotton, here is how we suggest making treatment decisions. First, select a minimum of 25 ten to twelve day old bolls that are still soft to the touch and can be crushed by hand. Select more bolls from at least two locations from larger fields. Crush these bolls and observe for internal injury. Note, it may make this process faster by first separating the bolls with external feeding signs from those that have none. First, crush the bolls with external feeding only and determine the percent that have internal injury. If a threshold is reached, then the remainder of the bolls with no external feeding signs will not need to be crushed. Internal damage may consist of one or more warts on the inside of the boll wall, damaged seed or stained lint. Second, the decision maker needs to know how long that particular field has been in the blooming stage. Most stink bug injury and loss is coming during weeks three though five or six of bloom. This is the period when most harvestable bolls are being set.

In Alabama, I suggest using a 10% internal damage threshold during weeks three though six of bloom. An insecticide application will usually suppress stink bug numbers for seven to ten days unless a field borders another untreated crop with high numbers of stink bugs. If has been my experience that stink bugs do not move rapidly across fields like plant bugs as they reinfest. The first four to ten rows adjacent to corn or peanuts seem to get most of the migration initially.

In our heaviest stink bugs years, cotton in the coastal plains of the southeast have required up to four applications. Under most conditions however, only two or three sprays may be warranted.

One last thing I will mention today is that, in the past, stink bugs seem to cause more internal boll damage in wet seasons than in dry seasons. That being the case, and unless the weather changes, we need to be extra cautious of stink bug damage to cotton in 2013.

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.