Since glyphosate-resistant water hemp and Palmer amaranth have been discovered in Texas in recent years, an exceptionally wet fall and winter and now spring season is causing concern that the growing season, while off to a good start, is also prime time for an exceptional uptick in weed problems across wide areas of Texas.
"Given that a single water hemp or Palmer amaranth plant can shed 500,000 to 1 million seed, one weed left in the field is too many," observed Texas AgriLife specialist and Nueces County agent Jason Ott in his latest weed report.
Texas A&M AgriLife Extension and Research has conducted numerous field studies to provide recommendations for managing glyphosate resistant weeds now that these populations have become more widespread.
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"Often, the most competitive weeds are those that emerge prior to, or at the same time as the crop. These weeds are quite effective at competing for the same consumable environmental resources such as water, nutrients, and sunlight that the crop seedling needs for healthy growth," Ott said.
It’s particularly important in cotton, which tends to have a slower growth rate as a seedling compared to other crops. Early-season competition is also highly detrimental to sorghum and corn seedlings. If these weeds are not controlled, significant yield losses can be expected.
Early weed growth
Ott reports excessive early season weed growth across Nueces County and all of coastal Texas from the southern tip to the Louisiana border. Large areas of the middle coast north into Southeast Texas already have received rainfall amounts this year that already exceeded annual averages. While the return of a rainy season has been welcomed by most, the consequence will be an exceptional challenge from weed growth.
"By controlling early-season weed infestations, the yield potential of the crop is protected. Additionally, emerged weeds are easier to control with post-emergence herbicides at this point. Later in the season, weeds can become hardened-off due to hot, dry conditions, and will be more difficult to control," Ott added.
While crop deadlines have passed for most if not all of South and Coastal Texas, county agents report planting continues in areas where wet fields have delayed operations in recent weeks.
As such, he warns that prior to planting, emerged weeds should be controlled with preplant burndown herbicides or tillage. Due to widespread problems with glyphosate resistant weeds in Texas, he recommends using a tank mix partner when applying glyphosate as a burndown, especially if the field has a history of glyphosate resistant weeds.
"Adding a soil residual tank-mix partner to burndown applications will provide some insurance against early season weed competition from later emerging weeds. Remember that rainfall, irrigation, or mechanical incorporation is required to move residual herbicides into the soil and activate them," he warns.
When using soil residual products, producers should be aware of the planting interval and crop rotation restrictions if planting intentions change. Also, the plant-back residual activity may not start until receiving an inch of moisture from irrigation or rainfall.
If these programs still don’t adequately control water hemp or Palmer amaranth, many options remain for managing them with post-emergence products. The key to POST herbicide efficacy is treatment timing. Ott says most applications will require treatment of pigweed species less than 4 inches tall.
Scouting is critical
He says it has become more important than ever to scout fields for weed escapes and treat them with alternative products. Texas AgriLife is not recommending elimination of glyphosate from herbicide programs; it is still effective on many of weed species. However, if glyphosate resistant weeds are a possibility, farmers should consider partnering glyphosate with other pre-plant, pre-emergence, and post-emergence herbicides.
In addition to problems from glyphosate-resistant weeds, Stephen Janak, County Extension Agent - Ag/Natural Resources in Colorado County, reports kudzu vines taking over a riverbank near Columbus, Texas.
After sending photos to rangeland specialists in College Station, the first establishment of kudzu in Colorado County has been confirmed. The report is not cause for panic, but landowners should be aware of the issue and should keep an eye out for this invasive plant.
Growing up to a foot per day, kudzu can take over an area seemingly overnight. Janak says many may recall the pictures from the southeastern U.S. where kudzu toppled power lines, covered barns and houses, and killed trees. Since it is growing on the riverbank, landowners need to make certain that seeds have not established elsewhere along the river and that birds or other animals haven’t planted the seeds elsewhere across the county.
Janak also reports recent discovery of poison hemlock in Colorado County. The weed was confirmed across the river from Kleimann Road south of Columbus. Poison hemlock is a non-native invasive referred to as the most poisonous plant known to man. Introduced from Europe, all parts of the plant are poisonous and should be avoided by humans. Livestock generally avoid the plant unless available forage becomes scarce. This biennial plant can be killed with 2, 4-D or similar broadleaf weed killer. It may be a good idea to remove livestock from the area after spraying, as weeds are more palatable as they wilt and die, and be aware to take care not to bale any of this plant in hay as livestock are more likely to consume it with the rest of the hay.