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Herbicide Injury as a result of Cool, Wet Weather Conditions

Posted: June 14, 2012

The cool, wet weather conditions we've been experiencing can result in herbicide injury to sweet corn. This post covers herbicide injury symptoms, how the weather can lead to herbicide injury and what to do if herbicide injury is a problem.
Elsa Sánchez and Bill Lamont, Penn State Horticulture and Extension

 

We’ve heard of cases in other states of wide-spread herbicide injury from preemergent herbicides applied to sweet corn this year due to cool, wet conditions. Since we’ve also experienced cool, wet weather we wanted to relay information on herbicide injury.

Herbicides for sweet corn

Below is a table of herbicides labeled for sweet corn. Injury from soil-applied herbicides is more commonly associated with cool, wet conditions and foliar-applied with hot, humid conditions. For more information on applying these herbicides see the product label. The Commercial Vegetable Production Recommendations guide Sweet Corn section (http://extension.psu.edu/vegetable-fruit/production-guides/2011-comercial-vegetable-guide/sweet-corn/view) also has useful information.

Useful preplant incorporated and preemergence herbicides for sweet corn grown in conventional tillage systems

Trade Name

Weeds Managed

Active Ingredient

HRAC Group*

Family

Sutan+ 6.7 EC

Annual grasses, yellow nutsedge, certain broadleaves

Butylate

8

Thiocarbamates

 

Combine with Atrazine to improve management of broadleaves

Preplant Incorporated or Preemergence

Micro-Tech or Intrro

Annual grasses, certain broadleaves (pigweed, nightshade, galinsoga), suppresses yellow nutsedge when preplant incorporated

Alachlor

15

Chloroacetamides

 

Combine with Atrazine to improve management of broadleaves

Dual II Magnum 7.64E (or OLF**)

Annual grasses, controls or suppresses yellow nutsedge, suppresses certain broadleaves

S-metolachlor

15

Chloroacetamides

 

Combine with atrazine or Extrazine to improve management of broadleaves

Atrazine 4FL (or OLF)

Broadleaves

Atrazine

5

Triazines

 

Combine with Micro-Tech, Partner or Dual II Magnum to improve management of annual grasses

Preemergence

Callisto 4SC

Common lambsquarters and other annual broadleaves, weak on ragweed and morningglory

Mesotrione**

27

Triketone

 

Combine with Micro-Tech, Partner or Dual II Magnum to improve control of annual grasses

Spike (leaf is tightly rolled and pointed straight up)

Prowl H2O (or OLF)

Annual grasses, certain annual broadleaves

Pendimethalin****

3

Dinitroanilines

 

Combine with Atrazine to improve management of broadleaves

Early Emergence

Atrazine 4L (or OLF)

Broadleaves

Atrazine

5

Triazines

Sandea 75WP (do not apply to ‘Jubilee’)

Yellow nutsedge, broadleaves (including common cocklebur, redroot pigweed, smooth pigweed, ragweed, velvetleaf); not effective on common lambsquarters, eastern black nightshade, only suppresses morningglory

Halosulfuron

2

Sulfonylurea

Aim 2EC or Aim 1.9EW

Broadleaves (including pigweeds, common lambsquarters, morningglory, eastern black nightshade, velvetleaf); not effective on ragweeds

Carfentrazone

14

Triazolinone

Laudis

Annual broadleaves (including common lambsquarters; triazine-resistant biotypes); many annual grasses

Tembotrione

27

Triketone

Impact 2.8SC

Broadleaves (including common lambsquarters, triazine-resistant biotypes); annual grasses

Topramezone

27

Triketone

Postemergence (annual grass management will be minimal)

Atrazine 4L (or OLF)

Broadleaves

Atrazine

5

Triazines

Basagran 4SC

Broadleaves

Bentazone

6

Benzothiadiazole

2,4-D 4EC

Broadleaves

2, 4-D Amine

4

Phenoxy

Stinger 3A

Certain annual and perennial broadleaves in Composite and Legume families

Clopyralid

4

Pyridinecarboxylic acid

Callisto 4SC

Common lambsquarters and other annual broadleaves, weak on ragweed and morningglory

Mesotrione

27

Triketone

Accent Q

Many annual grasses, certain broadleaves

Nicosulfuron

2

Sulfonylurea

*Herbicide Resistance Action Committee’s (HRAC) classification for resistance management

**OLF = other labeled formulations

**Temporary injury, appearing as whitening of the foliage after emergence, may occur. Rainfall or irrigation after planting and treatment, but before emergence, increases the likelihood of crop injury. Cold weather that slows corn growth will also retard recovery from injury following preemergence treatments. Sweet corn cultivars differ in sensitivity to mesotrione. The majority of cultivars exhibit slight injury symptoms when weather conditions after application are favorable. Certain cultivars are tolerant, while other exhibit more noticeable injury. Although no cultivar was severely injured by the recommended rate, postemergence application is preferred when weather conditions that favor injury occur at planting.

****cold wet conditions after application increase the risk of crop injury.

Symptoms based on herbicide active ingredient

One of the keys leading to a diagnosis of herbicide injury is that symptoms will occur across the area where the herbicide was sprayed, they will not be localized. Additionally, it will occur on all cultivars planted in the sprayed area; although, the expression of symptoms may vary by cultivar.

Metolachlor, alachlor and atrazine: Rarely, seedlings will produce leaves underground. Plants may have malformed, twisted leaves which do not unroll properly – called “buggy-whipping”. Plants will outgrow this injury once the soil dries out.

Mesotrione: Symptoms are yellowing or bleaching on leaves. Usually the older leaves are affected with newer leaves generally unaffected.

Butylate: Leaves will unroll improperly and be twisted.

Pendimethalin: Root tips will become clubbed or swollen. Leaves may be red or purple on margins.

Halosulfuron, nicosulfuron: Plants become stunted with yellowing of the new growth; yellow band across middle leaf.

Carfentrazone: Expect to see speckling on crop foliage after application. Initially the injury may appear to be substantial, but it is not systemic and corn will outgrow the injury rapidly.

Tembotrione, topramezone, mesotrione: Plant tissue bleaches.

2,4-D: Growing tips are yellow. Stems twist and have swellings. Leavers pucker, curl and wilt.

Bentazon: Yellowing between leaf veins is seen, followed by death of that tissue.

Clopyralid: Plants are stunted. Leaves are discolored and slight buggy-whipping is seen.

This website has pictures and descriptions of herbicide injury to corn for many of the active ingredients above: http://www.btny.purdue.edu/Extension/Weeds/HerbInj2/InjuryHerb1.html.

How cool, wet weather conditions can lead to herbicide injury

Herbicides are most effective when temperatures are between 70 and 85°F, when the crop and weeds are actively growing. When this is not the case the result can be crop injury, poor weed control or both. The process by which herbicides are degraded by the crop is highly influenced by temperature. When temperatures are cool (below 60°F daytime) plant metabolism slows down and so does herbicide degradation by the crop. These conditions can result in crop injury. Heavy rains soon after herbicide application can result in excess soil moisture and can be a problem if crop seed or shallow roots take up too much herbicide. Also, in some cases (butylate) the herbicide safener can be leached with excess moisture. Herbicide labels contain important information about temperature and moisture. For example, the DUAL II Magnum (metolachlor) label states that it “contains benoxacor which has been shown to enhance S-Metolachlor metabolism in corn. This enhanced metabolism can reduce the potential of S-Metolachlor injury to corn seedlings when grown under unfavorable weather conditions such as cool temperature or water stress.”

The crop will generally outgrow herbicide injury and if symptoms are not extensive, yield should not be affected. Postemergence herbicides can still be used, but consider delaying application until sweet corn plant growth is back to normal.