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Winter Annuals Ahead for Spring 2020

Winter Annuals Ahead for Spring 2020
By Delbert G. Voight, Jr
In the last few winter gatherings of growers, I have been approached with questions on dealing with how to manage winter annuals in grass hay, pastures, small grain, and alfalfa. We have missed some ideal weather conditions to apply appropriate pesticides for each crop this fall and mid-winter. There might be other openings if the weather cooperates to manage some of these issues. For this article, I will try to relate some management options. First of all is proper weed identification (ID) for this I would recommend using the Early Spring Weeds of No-Till Crop Production from the University of Missouri Extension.
Small Grains (Wheat, Barley)
In our wheat trials at the Southeast Ag Center we are seeing emergence and in some areas of the field they are at the same height as the wheat and can cause issues competing for light and nutrients.
To manage winter annuals in small grains there is a timing balance. Typically, growers would wait until we get some thistles growing (March or later) before applying a herbicide. This season the winter annuals (chickweed, dead nettle, shepherds purse and marestail) are growing aggressively and may need to be dealt with sooner than later if they begin to smother out the small grain. Another issue is with resistant bio types of chickweed that are ALS resistant this also lessens the options to manage the weed. For those without the resistant bio types Harmony Extra (group 2) continues to dominate the herbicide selection coupled with metribuzin (group 5) can be a plan to offer two modes of action and manage not gaining resistance in the field. The agronomy guide details the specific application instructions for use, but it is important to ensure that the proper adjuvants if required are utilized to ensure uptake into the plants. Starane Ultra (group 4) is an option for those with known resistance to ALS group 2 herbicides. The key is for growers to get out and scout and see if the population of winter annuals will need to be managed earlier than later.
Grass Pasture and Hay Fields
It is important to ID the weeds to manage. In this picture this is Star of Bethlehem and requires a different tactic to manage than winter annuals. (Del Voight, Penn State)
Another area where winter annuals are cropping up is in grass hay and pastures. What I have observed is mostly chickweed weed however ID is important. The picture is Star of Bethlehem and it is not a winter annual rather a bulb type perennial. If one misses the ID and uses the incorrect herbicide it will cause a failure. Having so many calls on chickweed I confirmed it in a few local pastures, and it seems to be growing well where the yellow foxtail was growing last season. There are effective materials for the winter annuals. Products such as Sharpen, Aim, Crossbow, Metsulfuron 60DF, and Overdrive are options for management, and they all have varying scope of weeds they control. Again, as in the case of Small Grains if it is ALS resistant then the Metsulfuron might not provide control and other herbicides might be the best option. Also, with Metsulfuron the reseeding is as long as 6 months so if one plans to overseed later this year they might find the seed will not come up. There are application specifications in the Agronomy Guide and should be consulted to ensure proper rate and adjuvant use. With the recent yellow foxtail (summer annual grass) outbreak many are planning to utilize Prowl H2O (only use the water-based formulation) and that treatment needs to be applied in March and again after first cutting for annual grass control in pastures. To manage both the chickweed and the Foxtail perhaps two products need to be applied to manage both. In a conversation with a large grower who would like to also overseed perennial grass into the pasture it can be done but it will take scouting and management. The label for Prowl H2O stipulates the grass needs to be established at the time of application. In reading the label it recommends after a cutting is considered established so keep that in mind as well. In this grower’s case he can overseed his pasture and once established which might be mid-May then apply the Prowl and other broadleaf herbicide to manage weeds. Also, the harvest restrictions for all products must be followed according to the label. It can be done but it will take additional scouting and grass ID to make it work.
Alfalfa Winter Annuals
Alfalfa with winter annual weeds.
Alfalfa is having similar issues to the other crops pertaining to the winter annuals that are growing and will continue to compete going into spring. There are some options within the dormant treatments that might prove effective this spring. In pure stands of alfalfa, there are numerous options to treat and again if ALS resistant chickweed exists there are numerous options to manage with other group herbicides. Gramoxone is an option that might set back the alfalfa a bit but works well in cooler but sunny conditions. Metribuzin, Pursuit, Raptor, and Chateau are also available. Prowl H2O also is available to manage potential grass outbreaks such as crabgrass and the foxtails. In the end, many options available and growers are encouraged to get out and check for which weeds are rapidly covering over and might compete this spring. In my travels, it appears the new seeding started this fall are tending to have the most competitive populations of winter annuals.
Now is the time to get out and see what might be an issue this spring. If growers identify an issue now there may be application windows opening up, so preparation is the key to responding to the openings presented in the coming weeks.
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