Indirect damage to vines from herbicides can occasionally be an issue on some sites, but a few simple steps will help mitigate the risks, writes Hutchinsons agronomist Will Robinson.
When it comes to the effects of herbicide damage to vines, there are two main aspects to consider; one is the impact of applications within your own vineyard; the other is the potential risks from certain actives that may be applied to neighbouring arable or pasture land.
In either case, vines are sensitive to many herbicides, with exposure resulting in issues like leaf curling, cupping, or wilting, poor berry formation, uneven ripening and potential yield loss.
Within the vineyard
Of course, the aspect that growers and vineyard managers have most control over is herbicide use within their own site.
During the dormant winter period, this often involves the application of a specific glyphosate formulation (Roundup Powermax) to help maintain the weed-free strip around and below vines that are more than four years old. Propyzamide is another option that can be applied up until the end of January, and may suit particularly weedy sites, and/or where growers want to reduce the reliance on repeated glyphosate applications, which they can select for less glyphosate susceptible weeds. Always follow label instructions regarding application conditions, water volumes, nozzle choice, forward speed, etc, and make sure sprayers are set up and maintained correctly.
All spraying equipment must be tested by an approved NSTS test centre before it is five years old, and after that, air-assisted sprayers must be tested every three years and small boom sprayers every six. Knapsack sprayers do not need testing, but should be regularly inspected by a competent person.
Once we move into spring and the warmer conditions typically experienced pre-flowering and post-flowering, extra care should be taken when applying any chemistry that volatilises easily, or is more prone to drift.
Carfentrazone-ethyl, for example, is prone to producing small droplets, which in certain conditions, can rise up to the canopy and cause ‘peppering’ of vine leaves (pictured), so it is best practice to include a suitable drift retardant to reduce this risk.
Avoid applications in high temperatures, and try to spray when there is a gentle breeze (3-10 mph), to keep air moving. Perfectly still conditions may seem ideal, but they can potentially increase the inversion potential and risk of crop damage.
Work with neighbours
The second aspect to consider is the risk of spray drift onto vines from certain herbicides that are being applied to any neighbouring land. In some situations, such as when carfentrazone-ethyl is applied to desiccate an adjacent potato crop, for example, this could pose a risk to vines in the rows nearest the field edge.
Another to watch is the broadleaf hormone herbicide 2,4-D, commonly used in many crops, notably sugar beet pre-emergence, and also on horse paddocks to control ragwort.
Even just a very small exposure to 2,4-D on one vine leaf, can result in damage to the whole plant, with leaves curling up, caps becoming stuck preventing berry set, and chlorosis appearing. Symptoms can look very similar to the Grapevine fanleaf virus (GFLV), and soil testing for the nematode that spreads GFLV is the main way to determine whether that is the cause or not. Generally, 2,4-D damage tends to affect isolated vines rather than whole blocks.
A good working relationship with neighbouring farmers and growers is the main way to manage and minimise any risks associated with spray drift into the vineyard. A good relationship where both parties understand the situation and can take appropriate steps to avoid any damage to sensitive crops before issues occur will make all the difference in the long run.
Drift out of the vineyard into neighbouring crops should not be overlooked either, especially if using actives that are only approved for use in GB and are not allowed elsewhere in Europe, such as dimethomorph.
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