ISSUE 1 May 13, 2010
A BANNER YEAR FOR COMMON MALLOW
It appears that common mallow is "common" again this year which brings the question of which management practices are best for control. Mallow can be an annual or biennial so it can develop a deep tap root. As with most biennials, killing 1st year plants is easier than trying to kill mature, deep rooted plants the second year.
Mallow is a problem in Canada and the Canadian Weed Control Guide can give some clues about effective herbicides. There are essentially two herbicides that are effective. The guide shows products containing fluroxypyr (Starane) give E common mallow control. Sulfonylurea herbicides similar to Harmony Extra type products (thifensulfuron + tribenuron) are the other alternative but control shows only F. No distinction is made between seedling and mature plants for the ratings.
Our ND Weed Control Guide shows F-E for several products containing fluroxypyr but also shows G-E for the Harmony Extra type products. These ratings are somewhat different than the ratings in the Canadian Weed Guide but are based on observations from NDSU weed scientists. Any method to enhance and optimize herbicide activity through effective adjuvants and nitrogen fertilizer as allowed on the label is recommended. Application to smaller, seedling stage plants will be more successful than larger plants.
For Roundup Ready crops, glyphosate will give P to E (probably due to differences in plant stage) and Ignite in Liberty Link crops will give G control of mallow.
It is better to do some kind of control practice because, as with perennial weeds, if you do nothing it will just get worse.
Extension Weed Specialist
THE PESKY DANDELION
Dandelions are more prevalent in crop fields than ever before. Dandelions have likely become more prevalent due to reducing the frequency and depth of tillage operations, reduced usage of preemergence herbicides, especially in soybean, and allowing dandelions to survive in field borders.
Control of dandelion is best achieved with fall herbicide applications. However, it was extremely difficult to apply herbicides last fall, forcing control of dandelion this spring. Control of dandelions in the spring with preplant herbicides is highly variable and few products are available.
Glyphosate (1.5 lb ae/A) [see page 71 of the 2010 North Dakota Weed Control Guide for rates of many glyphosate formulations] plus Express SG (0.33 to 0.5 oz/A) plus NIS (0.25 %v/v) plus AMS (8.5 lb/100 gallon of spray solution) should provide the most effective dandelion control in the spring. This herbicide treatment must be applied at least 14 days before planting of corn and soybean and can be applied up to prior to emergence of cereal crops. Generic formulations of tribenuron must be applied 45 days prior to planting of corn and soybean. Adding 2,4-D ester (0.5 lb ae/A [1.0 pt/A of a 4 lb/gallon product]) to glyphosate may improve dandelion control compared to glyphosate alone, although not guaranteed. Planting of soybean must be delayed at least 7 days if 2,4-D is applied. If planting can not be delayed, then glyphosate applied prior to planting at 1.5 lb ae/A or greater plus AMS (8.5 lb/100 gallon of spray solution) should provide adequate control, although postemergence (POST) herbicides will be required to improve control. Lower rates of glyphosate could be applied prior to planting of corn and cereal crops as long as effective POST herbicides are applied. In soybean no POST herbicide will effectively control dandelion, therefore application of the highest rate of glyphosate is suggested to maximize dandelion control.
For wheat and barley, WideMatch, Curtail, and Express (0.5 oz/A) plus 2,4-D or Curtail applied POST should effectively control dandelion. For corn, Distinct and Status applied POST at high rates will likely provide effective dandelion control. Callisto, Impact, or Laudis mixed with atrazine usually provides quick and effective control initially, however, plants will likely recover over time. Glyphosate applied at maximum POST rates to Roundup Ready (RR) corn will provide additional suppression of dandelion. Ignite 280 applied POST to Liberty Link corn will provide some control of dandelion. For RR soybean, glyphosate applied POST at 1.5 lb ae/A followed by glyphosate at 0.75 lb ae/A will provide the best dandelion control. Adding FirstRate with glyphosate in RR soybean can improve dandelion control, but may not be cost effective.
Additional information about dandelion control can be found on the web at http://www.ag.ndsu.edu/weeds/weed-year/Dandelion.pdf or on page 134 of the 2009 North Dakota Weed Control Guide. Additional information can also be found on page 67 of the 2010 North Dakota Weed Control Guide.
Agronomist - Weed Science