Lack of soil applied herbicides, herbicides applied later than recommended, flushes of weeds emerging after application, poor weed control, and favorable weather conditions promoting weed growth have resulted in several weedy small grain fields. Producers may be asking about harvest aids to use to burn down these weeds prior to harvesting the crop. It is important to keep preharvest weed control in small grains in perspective. The following are some factors to consider before applying a herbicide as a harvest aid:

• The expectations for preharvest weed control usually exceed reality - it is not possible to kill/dry down a 3-foot weed in the same manner as a 3-inch weed. Lower portions of the weed may not be affected.

• It requires time to dry down treated weeds - usually 7 to 10 days. It may require more time if wet and/or cool weather conditions occur after treatment. All herbicides labeled for preharvest application are systemic and slow acting which requires a longer dry down period as compared to contact, fast acting herbicides.

• The intent of a preharvest treatment should be to facilitate harvest and reduce harvest loss. Preharvest treatments do not decrease yield losses if applied in the prescribed application window. Realize that yield loss has already occurred from weed competition and weed seed production will add to next year’s weed problem.

• If only dry down of grain straw and grassy weeds is desired then rates of 0.5 to 1 pt/A of Roundup type products are sufficient. Higher rates of 1 qt/A are needed for dry down and control broadleaf weeds like kochia and nightshade, and perennial weeds.

• Herbicide drift from preharvest treatments can cause major problems this time of year. Consider sensitive cotton and other plants (trees, gardens, etc.) in the general vicinity of the field receiving treatment.

NOTE: There are no herbicides labeled as a harvest aid for use on oats. Gramoxone Max (paraquat), Harmony Extra, Curtail, Express, Peak, Canvas, or Amber are NOT labeled as a harvest aid in small grains. They are illegal.

Table 1. Recommendations for Harvest Aids in Wheat
Harvest Aids	Product Rate/Acre	Weeds Controlled	Harvest Restrictions	Crop Application Timing	Remarks	Tank Mixes	Mode of Action
Ally	0.1 oz	Annual broadleaf weeds	A waiting interval of 10 days is required before harvest.	Apply after hard dough stage of grain (less than 30% moisture).	Always apply with a non-ionic surfactant. Do not use in soils with a pH exceeding 7.9. Weeds growing under limited moisture may not be controlled. Do not use straw for livestock feed.	2,4-D, Clarity	ALS
Clarity	0.5 pt/A	Annual and some perennial broadleaf weeds	A waiting interval of 10-14 days is required before harvest.	Apply when wheat is in the hard dough stage and the joints of the stem are no longer green.	Do not use pre-harvest treated wheat for seed unless a germination test is conducted. Do not allow grazing or use of feed from treated area.	Ally, 2,4-D, Roundup	Growth regulator
Glyphosate Roundup Touchdown	0.5-1.0 qt 0.5-1.0 qt	Annual and some perennial broadleaf and grass weeds	A waiting interval of 7 days is required before harvest.	Apply after hard dough stage of grain (less than 30% moisture).	Do not exceed 1 quart/A. Not recommended for wheat being harvested for seed. Do not feed treated straw or permit dairy or meat animals being finished for slaughter to graze treated grain fields within 2 weeks after treatment.	2,4-D, Clarity	ALS
2,4-D 2,4-D 4 Low V Ester	1.0-2.0 pt	Annual and some perennial broadleaf weeds	Do not allow dairy cattle or slaughter animals to graze for 2 weeks after treatment.	Apply after hard dough stage of grain (less than 30% moisture).	Do not used treated straw for livestock feed.	Ally, Clarity, Roundup	Growth regulator
Mode of Action Defined Mode of Action is the primary biochemical or biophysical event that a herbicide directly affects and results in the death of the plant. ALS herbicides inhibit the pathways leading to amino acid production in plants. Growth regulator herbicides disrupt hormone balance and protein synthesis in the plant leading to weak cells walls and rapid cell proliferations.

Kernel weight and germination were affected only by glyphosate applications at the milk stage. Kernal Weight reductions ranged from 19 to 73% and percent germination was reduced by 2 to 46%, compared to the untreated wheat. Wheat seed planted the following year from the glyphosate treatment applied at the milk stage resulted in seedling density reductions ranging from 28 to 99%; reduction in plant height of 19 to 39%; and a reduction in seed yield of 12 to 97%, compared to seeds from untreated wheat. In this study, wheat seed and seedling quality following preharvest glyphosate applications were most greatly influenced by crop maturity stage at the time of application than by herbicide rate or variety.

I would expect similar impacts to hard red winter wheat as those reported by Yenish and Young. If glyphosate is used as a harvest aid: 1) make sure the wheat is mature (hard dough stage), and 2) Don't keep the seed for replant purposes.