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Weather Forecast

Apr 17, 2017

Wheat Update

Wheat in Hill and McLennan Counties ranges from the start of grain fill to soft dough. We've been drenched again with more rains last Tuesday, and I'm concerned that these rains will cause nitrogen loss issues like they did last year for the corn. There is already yellowing in the low spots of some fields.

Some wheat fields may be experiencing damage from fall armyworm, but populations will vary greatly by location. We also still have a huge abundance of natural enemies that could be helping keep them in check, as well as the scattered aphid populations. Ladybugs, lacewings, and spiders can be found readily in most fields and will hopefully persist to aid us in other crops.

Leaf rust continues to spread in most fields, but wheat is past the flowering stage and is less vulnerable to yield losses. In fields that were not treated at Feekes 10, pockets of rust can be seen covering the flag leaves.

Leaf rust on flag leaves.

All species of stinkbugs can be found feeding occasionally on wheat heads. Seeing a few is not a cause for alarm, and generally they do not reach threshold levels. 

Eastern leaf-footed bug
Conchuela stink bug
Brown stink bug

Mar 14, 2017

Leaf Rust and Wheat Update

Wheat Growth

Wheat crops across the US continue to grow at an accelerated rate. Most of the wheat is in Feekes 8-10 (flag leaf to boot), and a field in the scouting program is already 50% headed as of today. Compared to last year, that puts us about 2 weeks or more ahead of schedule: in 2016, we had most fields in boot on March 28th.

We had a bit of a frost in some places last night, and some wheat in the more vulnerable stages could have been affected.

Leaf Rust

The unusually warm winter and periodic rains have resulted in high disease pressure this year. Stripe rust can be found in some fields, but in fields that were not treated at topdress (Feekes 5-6), leaf rust has increased significantly. Some fields remain completely clean, and others show pustules up to F1 leaf (just below the flag leaf). Fields with very heavy rust pressure may benefit from a treatment at Feekes 10 or before.

You may have heavy leaf rust in your wheat field if you come out orange after scouting.
Rust should be kept off the flag leaf, which contributes to 75% of the yield. At flowering, if there is 10% of the flag leaf surface covered by rust pustules, you can expect a 10% yield loss.

In this section of a leaf, pustules cover about 1% of the total leaf area. However, the yellow, necrotic areas are unable to photosynthesize and will also contribute to yield loss.

Mar 8, 2017

Threat of Freeze

According to the National Weather Service, we are now in ENSO-neutral for spring 2017 (La Nina ended in February, and they predict El Nino conditions to return after the summer). The prediction for above average temperatures continues throughout the spring. The wheat crop in Texas and other states is greening up much more quickly than normal. Some fields are already at Feekes 6-7 (jointing), which is the stage where the growing point rises above the soil surface. This leaves the growing point vulnerable to damage, especially freeze damage. There are even a few off-type plants in most fields that have already headed out and flowered. I've also heard of a wheat field in the Blacklands that is already 50% headed. 

There's always the possibility that we could not have a freeze, or temperatures won't be low enough for long enough to affect the plants. The chart below shows what stages of wheat can be injured by freezing temperatures. At least 2 hours of these temperatures is needed to cause injury.

Feb 9, 2017

Sulfoxaflor Emergency Exemption

Sulfoxaflor (Transform) has been granted an emergency exemption for use on sorghum (targeting the sugarcane aphid) in 2017. You can read the details here.

Both Sivanto and Transform are highly effective against the sugarcane aphid (SCA) in sorghum where other aphid insecticides tend to fall short. Having both chemistries in our tool belt is vital to slowing the development of resistance. Sivanto has longer residual action, up to 3 weeks or more in the right conditions.

SCA move to the heads as the sorghum plants reach maturity. This is possibly because the nutrient availability in the plants change or the leaves lose moisture. 

Brief SCA Review for 2017

Managing the SCA truly requires an integrated approach. With recent developments in variety selection for tolerance to SCA, its starts with making the right choice in seed. In 2016, over 20 varieties have been identified as being tolerant or resistant to SCA: either SCA populations don't develop as quickly on these varieties, or they can withstand much higher infestations without yield loss than susceptible varieties. Varieties don't always preform the same in one region to another, so be sure to reference local data as much as possible when selecting them.

The next important decision to make is planting timing. Research and field observations consistently show that earlier planted fields have fewer SCA problems and can often avoid being treated at all. Seed treatments also play a large part in early season infestation levels.

Because SCA reproduce so quickly in the right environment, scouting fields on a regular basis is key to preventing yield losses. Populations can literally go from in the 20's per leaf to in the 100's within a week. Some research from Georgia shows that a treatment delayed by 5 days can cause a 75% reduction in yield compared to a timely spray.

It is unclear what kind of effect biological control plays on SCA populations at this time. Due to the sheer number the aphid can produce, and the fact that SCA are rarely parasitized by wasps, natural enemies may not be able to suppress them at certain levels. However, choosing the right treatments and keeping impacts on beneficials low is still important.

As grain sorghum nears harvest, some producers choose to desiccate entire fields instead of applying insecticide. This method has many benefits: no insecticide pressure means lower chance of resistance development, usually aphids don't have time to move into the head and create honeydew build-up, and it allows for timely harvest. However this does not fit every field in every situation and heavily depends on timing.

These few plants were missed by the glyphosate applications. SCA flocked to them as the only source of food in the field and they became drenched in honeydew.
If you need help making an "attack plan" for SCA this season, your local AgriLife office has specialists and agents on hand to answer any questions.

Feb 8, 2017

Blacklands Pest Update

Wheat in Hill and McLennan Counties ranges from Feekes stage 2 through Feekes 5, just before noding (see chart below for reference). We have good soil moisture and no standing water issues, and the wheat is tillering well. Temperatures fluctuate week to week, with near freezing to in the 80's within a few days. Such is Texas weather!

Low levels of leaf and stripe rust can be found just about everywhere, but are restricted to the lower leaves and are much reduced in fields that were sprayed with fungicide at topdress. Fungicide residual control, depending on the product and environmental factors, usually lasts about 3 weeks.

Stripe rust is a light yellow color and can typically be seen in long stripes following the leaf veins.

Leaf rust on wheat. Leaf rust pustules are a dark orange color and scattered about the leaf.

Flecking (the light spots on this leaf) can indicate a resistant response to disease. The plant cells around the fungal pustules die, preventing them from spreading. Flecking occurs naturally on some varieties and may not always be a sign of disease.

No signs yet of septoria or tan spot, which don't usually cause concern here in the Blacklands, or powdery mildew.

Several fields that didn't receive insecticide at topdress have larger populations of the bird cherry-oat aphid (BCOA). This aphid does not inject a toxin as it feeds, like the greenbug, but can spread barley dwarf virus.
BCOA can be recognized by their dark green color and distinct reddish spot on their abdomen. Photo from Oklahoma State University Extension.

It takes a rather sizeable infestation of BCOA to justify a spray: Oklahoma State entomologits suggest a threshold of 20 per tiller on average. It's also reasonable to use the same thresholds for greenbugs here, though greenbugs cause considerably more damage as they feed. Wheat can typically tolerate BCOA feeding very well, and their populations are usually controlled by predators and parasitoids.

Speaking of which, ladybeetles and parasitized aphids (mummies) abound in their infested fields as well.

A rather cheeky ladybeetle laid a cluster of eggs on this henbit. Good thing that the newly hatched larvae can travel a short distance to find food.
We seem to have fairly typical levels of weeds in wheat with no resistance problems or herbicide failures reported so far. Common weeds in the scouting program fields include henbit and ryegrass, which are being controlled as topdressing continues.

If you have any questions or need help with pest issues, don't hesitate to contact your local AgriLife office via e-mail or phone.