Wines & Vines

March 2015 Wines&Vines 27 grounded grapegrowIng Winter weeds germinate with fall rains, overwinter as a small "basal rosette" and then bolt in the spring. Warm soil temperatures germinate a second set of summer weeds. In both cases, early spraying is essen- tial for best control. Most herbi- cide programs are based on two types of materials. Post-emergent herbicides are applied after the weeds have emerged. Glyphosate (Roundup), paraquat and carfan- trazone-ethyl (Shark) are examples used in vineyards. Pre-emergent herbicides control weeds as they are germinating, or just after ger- mination when they are very small. Examples include oryzlin (Surflan), flumioxazin (Chateau) and isoxa- ben (Gallery). If you can apply materials before (pre-emergent) or just after the weeds have germi- nated (both pre-emergent and post-emergent), and before leaves have fallen from the vines, you will get very good results in controlling weeds. If the leaves have fallen, University of California weed sci- entist John Roncoroni has shown in test plots that sweeping the leaves and other trash out from under the vines creates better re- sults. When weeds are small and there is little leaf litter beneath the vines, you can also control them with flaming (you are essentially wilting the small seedlings, not set- ting them on fire.) If your vineyard is flat, you can also hill soil over the small weeds and pull the soil back later in spring—this tech- nique is used by many organic growers. In all cases, controlling weeds while they're small requires less effort and herbicide. Best control with pre-emergent herbicides may require two ap- plications, depending on the weeds present and the weather. A fall ap- plication made after harvest (No- vember-December) and again in late winter (February) may be needed in areas with high rainfall. A single application in winter (January and February) with both pre- and post-emergent herbicides may be effective in drier areas, but it may require additional weed control in the summer such as spot spraying, hoeing or mechanical weed control. Mixing both a pre-emergent and post-emergent herbicide and Custom made - Handcrafted Barrels Weed-control strategies Start clean: effective vineyard weed-control programs start before the vineyard is even planted. If you know that you have some difficult weeds, eradicate them before planting. Very bad actors that should be controlled include Bermuda grass, Johnson grass and nut sedge. there are many effective herbicides that can do the job, but be very careful about plant back effects—some herbicides control tough weeds, but they may also make growing grapevines nearly impossible for several years. (materials such as oust, trans- line and others have residual activity that is very toxic to vines.) Work with a knowledgeable pest control advisor (PCA), extension farm advisor or other weed-control specialists to evaluate your weed problems and how best to control them. For people who don't want to use herbicides, a strategy of repeated tillage, competitive annual crops and fallowing the land can be very useful to reduce weed pressure. Don't bring in problemS: make sure that any soil amendments (compost or other organic matter) do not have weed seed in them. raw manure that hasn't been well composted is a classic source of bad weeds. If you are planting cover crops or field crops prior to installing the vineyard, make sure that your seed source has been tested and found to be free of noxious weeds. If you are planting containerized nurs- ery stock, don't accept anything with weeds growing in the pots. plant clean: make sure that weeds are under control before you plant your vines. you can use till- age, pre- and post-emergent herbicides (that can be safely applied) before and after you plant to keep the area free of weeds to get your vines off to a great start. Herbicides are tricky; be sure you are working with someone who can give you the right information about their use so that you don't unintentionally do dam- age to your newly planted vines. pay attention to what iS growing in your vineyarD: It doesn't take long for new weed species to get a toehold, and many can be stopped if you are watching for them. Small populations should be hoed out and physically removed from the vineyard. larger infestations should be put on an eradication program of an appropriate herbicide or tillage program earlier rather than later so they don't become a much bigger problem in the future. plan on uSing multiple StrategieS: the idea that you can use the same approach to weed control year after year will most likely be unsatisfactory in the long run, as there will always be some species that can tolerate whatever approach you are taking. A good example is a roundup-only program. We now have several weed species that are tolerant of this herbicide and require other materials to keep weeds in check, such as tank mixes with pre-emergent herbicides, mechanical cultivation or hand hoeing.

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