Over the past eight days, Soybean Aphid populations in the Alexander, IA area have been increasing dramatically.  I’ve been monitoring the aphid populations for the past several weeks and noticed a significant increase in numbers on August 6th. That day, I started to intensify my scouting methods and focused on soybean fields for Latham Farms especially. I adhere to the economic threshold of 250 aphids/plant on 80% of the plants through podset. In every field that I scouted on the 6th and 7th, I found populations to be below threshold. A few were in the 40-50% category but most were at 25% and less. In many areas, it was difficult to find individual plants that were at or close to threshold.

That changed drastically over the next 3-4 days! I started scouting again on Tuesday and was amazed to find all but one of the fields at economic threshold and that one was at 75%. Obviously, we made the decision to apply an insecticide to those fields and work began that next day. Over the past two days I’ve received similar reports from Latham production growers in our area and other farmers as well. It would appear that most soybean aphids in our immediate area will be treated with an insecticide soon if they haven’t been already.

One word of caution! If your soybean fields are not at threshold, don’t be tempted to spray an insecticide too quickly. I’ve already received several reports of farmers who went ahead and added an insecticide to their last application of glyphosate herbicide just because it was “convenient” to do it at that time. These farmers are now spraying an insecticide again to control the aphid population that exploded in the recent week. Essentially, when they sprayed the first time, they killed whatever beneficial insects were in their fields at that earlier time leaving the door wide open for aphids from the neighboring fields to infest theirs!

By the way, over the years I’ve developed my own method of speed scouting for Soybean Aphid. If you’re having trouble following other methods, contact me and I will explain what I do.

There are a number of online sources starting to report that conditions may be favorable for soybean rust to hit Midwestern fields this season. Iowa State University Extension runs a site called The Rust Report. A recent posting on June 17 reported that “…Alabama’s extension soybean pathologist said that soybean rust was 3-4 weeks ‘ahead of schedule,’ and it is farther north than in previous years. Georgia’s soybean pathologists said that ‘these early finds mean that soybean rust could be a real threat to the soybean crop if the disease continues to progress.’”

As Daren Mueller, a member of ISU’s soybean rust team, reports, ag specialists in the south earlier in the year were seeing soybean rust appear on kudzu. Kudzu is a vine plant that is loved and hated in Georgia and Alabama. It’s a pest plant that proliferates around abandoned buildings, yet can also be fed as temporary, high-quality forage that cattle tend to like. Earlier this month, some low level rust was found in a kudzu patch in Georgia. That finding has now been updated to include some rust found on southern soybeans. Weather conditions may be favorable for the rust to spread in the Southeastern states. That means we should be on the lookout in the Midwest as growing season progresses.

The Rust Report provides a lot of helpful information on management of soybean rust, how to spot it, how to make sure it’s rust and not a look-alike disease, and many other tips.

According to Stop Soybean Rust.com, “the main effects (of rust) on the soybean plant are destruction of photosynthetic tissue, which in turn causes premature defoliation, early maturation, and severe yield reductions through reduction in the number of pods and seeds, and decreased seed weight.” So close monitoring and information sharing is essential as rust moves out of the South.

Be assured we’ll keep you updated on any notable developments.

Latham is a partner in the Iowa State University Extension Corn and Soybean Initiative. That means we get timely alerts when any farming condition emerges that could impact a number of growers.

We recently received an alert about possible emergence of black cutworm in Iowa. The alert is reproduced below. Also, we have a simple spreadsheet calculator available for estimating stand-loss threshold of black cutworm as insecticide is applied.

Just give me a call at 1-800-798-3258 or email me at mark@lathamhybrids.com and I’ll be glad to send you the calculator document and explain it to you. For example, one simple calculation on the spreadsheet shows a corn stand planted at 32K plants per acre with an expected yield of 200 bu/acre at a market price of $6 per bushel and receiving insecticide application at a cost of $15/acre could realize an estimated loss of 400 plants per acre, or 1.25%.

Black cutworm to start cutting May 24: scouting is advised

From Iowa State University Extension Corn and Soybean Initiative

Black cutworms could start cutting corn May 24-26 in the southern two-thirds of Iowa, and the first week of June in the northern three tiers of counties. Growers should scout for cutworms as soon as corn emerges, paying special attention to late-planted or weedy fields.

Most at-risk fields:

• Late-planted
• Reduced tillage
• High weed populations – especially of winter annuals
• Near natural vegetation areas
• Poorly drained or low-lying, such as in the floodplain of a stream or river.

Damage signs
• Small, irregular holes in leaves (from young, above-ground larvae feeding)
• Cut stems or clipped leaves (from older larvae, in 4-6 instar – usually feed underground at night)

When scouting

• Examine 250 plants (50 plants in five locations) weekly until corn reaches V5.
• Check for wilted, discolored or damaged leaves and missing plants.
• If damaged leaves are found: dig around the base of the plant and look for larvae. If soils are dry or crusted, larvae  may burrow to moist soil and move to new plants.
• Flag suspected “hot spots” and monitor larval feeding (or lack of it) for a few days.

Economic Threshold & Treatment Options
•Economic thresholds for black cutworm were adjusted last year due to higher crop value and corn stands.
•A tool to calculate treatment thresholds for stand loss will be published in ICM News next week.

To tell black from dingy cutworm larvae

Both feed on corn, but dingy cutworms rarely cut leaves. Black cutworms have two prominent tubercles (dark bumps) of differing sizes on each body segment; dingy cutworms have two of the same size.

Long story short: Black cutworms may start cutting corn May 24 in the southern two-thirds of Iowa. Scout for corn as soon as it emerges, especially in late-planted, weedy or reduced tillage fields. Use the attached threshold calculator to determine the best treatment for your fields.

Source: Erin Hodgson and Jon Tollefson, ISU Department of Entomology