LOVELOCK - I frequently receive questions about how to identify weeds and what the best resources are for help with identification.
It is important to remember that the first key to weed management is proper weed identification. The best method for timely identification is through field scouting. This includes scouting your vegetable garden and/or lawn.
If you applied a pre-emergent herbicide (a herbicide that prevents weeds from germinating), then you should check for the presence of weed within two weeks after crop emergence to evaluate herbicide performance and to determine if there is a need for weed control, such as hoeing, cultivation or post-emergence herbicides. Earlier scouting is essential for proper weed control.
When scouting for weeds, identify and record all weed species found. Determine the severity of the infestation by counting the number of weeds found per 10 feet of row for large infestations or per 100 feet of row for smaller infestations in all areas sampled.
Sample areas should represent no more than five acres, so sample enough areas to get an accurate count of the different weeds present in the field or on the farm. The approximate height and growth stage of both weeds and crop should be recorded.
Time of weed emergence, variations in local environment (soil and weather), and degree of post-emergence weed control will affect weed-crop interference. Different weeds have different effects on crop yields.
It is always important to determine the "economic threshold" for weed control. An economic threshold for weeds is the density of a weed population at which control is economically justified because of the potential for yield reduction, quality loss, harvesting difficulties, or other problems that weeds may cause.
Some general assumptions about weed-crop interference can help make the appropriate management decision. Weed-crop competition studies indicate that if weeds are allowed to grow with most field crops under normal environmental conditions for no longer than four to six weeks after crop emergence and are then removed, and if the crop remains weed-free until harvest, then yield reduction is unlikely.
In addition, if weeds are kept out of the field for four to six weeks after crop emergence, any weeds that later invade will not reduce yield significantly, although they may produce seeds, cause harvesting problems, or reduce crop quality.
Along with weed reports, early soil moisture observations are important. They serve as indicators of herbicide effectiveness. Adequate moisture is necessary for effective weed control with all soil-applied herbicides. Too little rainfall can mean there is not enough moisture to allow adequate mobilization of the herbicide; too much rain can cause more soluble herbicides to move downward below the zone where they are most effective.
Post-emergence herbicides usually are most effective when weeds are young and actively growing. The degree of control with these herbicides will vary due to differences in weed species, growth stages, weather conditions, and herbicide application method. To select the best possible herbicide and apply it at the optimum time to maximize control, you need to be able to identify weed seedlings when they are small.
There are many resources available for plant identification, but these are some of the ones we use the most.
1. There are Apps for weed identification.
• "ID Weeds" from the University of Missouri Extension. A little technical; however, a solid weed list with a good vocabulary. Although this App may not list all the weeds we have in Nevada, it may help to get you heading in the right direction. http://weedid.missouri.edu/.
• "Weed ID" by BASF. This one has a "take a picture" option that can be very helpful. It also has general ID pictures instead of just terms when choosing characteristics. https://itunes.apple.com/us/app/weed-id/id506639384?mt=8
2. Weed ID on the Internet.
Many weed ID websites are available, and the best one is really a matter of personal preference.
This resource is from the University of Nevada Cooperative Extension, "Weed Identification and Control Guide," http://www.unce.unr.edu/publications/files/nr/other/eb9801.pdf.
A favorite for just looking at photos of weeds is http://images.bugwood.org. The "images" tool in Google is also very helpful for confirming a weed ID.
3. Books/CDs.
Yes, they still make books and they are one of my favorite resources for weed identification. My top pick is "Weeds of the West" published by the Western Society of Weed Science and co-sponsored by Cooperative Extension of the Western States. Also, "Broadleaf and Grass Weeds of the West."
"Identification CD Combo Pack" developed by Joseph M. DiTomaso, a Cooperative Extension weed specialist in the Department of Plant Sciences at the University of California, Davis.
The two-CD pack contains over 4,000 color photographs and illustrations of 754 broadleaf species and 231 grasses. The weed identification software is an interactive program that is easy to run and uses plant characteristics to identify weeds.
So, if you need any assistance identifying problem weeds feel free to contact your local Cooperative Extension Office, or use one of the many resources identified above.[[In-content Ad]]
