Farm Progress

Arkansas wheat crop developing rapidly.Large portion of state in drought.Glyphosate drift on wheat increasing problem.Stripe rust found in crop. 

April 8, 2011

5 Min Read

On Thursday, the latest Arkansas Wheat Newsletter was released. Included in the University of Arkansas Division of Agriculture release is a review of current crop conditions, glyphosate drift issues and disease.

Wheat overview

From Jason Kelley, wheat and feed grains Extension agronomist:

The wheat crop continues to make rapid growth development. According to the April 4Arkansas Agricultural Statistics Service crop report 5 percent of the wheat crop had headed, which was near the 5-year average, but ahead of last year’s pace.

Dry weather continues across the state with nearly all counties being classified as being in a drought. However, the dry winter and spring so far has been beneficial to our wheat crop with 68 percent of the crop being reported in good to excellent condition.

Stripe rust has been found in multiple locations in central and southeast Arkansas (the first week of April). Stripe rust levels within infected fields have been low in most instances; however hot spots have been found in susceptible varieties in Desha and Arkansas counties of Southeast Arkansas.

Wheat varieties that stripe rust has been found on include: AGS 2060, AgriPro Beretta, AgriPro W-1377, Armor 260Z, Armor Renegade, Dixie 427, Hornbeck 3266, Progeny 185, and Ranger.

Glyphosate drift complaints have been widespread with many of the calls coming from central Arkansas this week.

The Wheat Research Verification program summary below provides a good indication of growth stages, foliar disease and glyphosate drift incidence that we are seeing in wheat fields across the state at this time.

Glyphosate drift on wheat

From Bob Scott, Extension weed scientist:

Unfortunately, it appears that one of the most common problems for wheat producers this year is not a weed or other pest, but the occurrence of glyphosate drift. Damage reports first started coming in from the southern counties over two weeks ago, as wheat begins to head further north reports from county agents are coming in like a roll call from south to north. I cannot begin to estimate the number of acres affected at this time, from my cell phone it seems like all of them.

If you are familiar glyphosate drift on rice, you know the effects of glyphosate drift to wheat. During tillering effects of small amounts of glyphosate on wheat can cause stunting, chlorosis and some dead leaves and tillers; however, prior to jointing this damage does not effect seedhead or flagleaf development. If drift, even small amounts, occurs after tillering and after joint formation begins (like green-ring in rice), the damage is basically invisible until the flagleaf emerges. Flag leaves will be stunted (a symptom of almost no other ailment in wheat), bleached to striped white or yellow chlorosis, often twisted at the base of the flagleaf where it attaches the stem. If the flag leaf is damaged, a damaged head almost always follows. This can resemble the effects of late applications of 2,4-D as seedheads get "caught" in the collar region and can emerge sideways from the sheath.

There is no cure for glyphosate drift damage. Damage can range from 5 percent to 100 percent depending on severity of injury, which depends on rate and timing. It is proving difficult to find the source for many of these drift calls.

Just a reminder: this is the job of the Arkansas State Plant Board(501) 225-1598.

Disease update

From Gene Milus, plant pathologist:

The most serious disease at this time is stripe rust on susceptible and very susceptible varieties where the disease overwintered and formed hot spots. Fields with hot spots should be sprayed with a fungicide as soon as possible. Fields of varieties with a susceptible reaction type (abundant yellow sporulation surrounded by green leaf tissue, see photos below) but without hot spots at this time should be the next highest priority for being sprayed. Fields of varieties with only resistant to moderately resistant reactions (little or no yellow sporulation surrounded by yellow or tan leaf tissue, see photos below) are not likely to have significant losses from stripe rust, and applying a fungicide may not be necessary to control stripe rust.

There have been no new reports of leaf rust since the previous newsletter. Recent dry weather is keeping Septoria leaf blotch and Stagonospora blotch confined to the lowest leaves that were infected last fall or earlier this spring. Frequent rains will be needed for these diseases to move to upper leaves.

The overall incidence of barley yellow dwarf appears to be low. If symptomatic plants are scattered and not stunted, then the infection likely occurred during the spring, and yield losses should be insignificant. If symptomatic plants are in stunted patches, then infection occurred last fall and yield losses likely will be significant in the stunted areas.

The risk of scab remains low across Arkansas south of I-40 where wheat has flowered or is approaching flowering. Flowering is the most favorable time for scab infection, and dry conditions are not conducive for spore production or infection. Given the recent dry conditions, several rainy periods will be needed to elevate the risk of scab.

Syngenta recently registered Alto 100 SL fungicide (Cyprocanazole) for use on wheat and it has been used this season on wheat in southwest Arkansas. Recommended rates are 3 to 5.5 fl oz per acre. It likely is effective on rusts, Septoria leaf blotch, Stagonospora blotch, and powdery mildew but not effective for scab.

For more information, contact your local county Extension agent or e-mail the authors at [email protected], [email protected], or [email protected].

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