Improving Application in Vegetable Crops
Key challenges for application include waxy surfaces and dense canopies
Vegetables are a very variable group of spray targets. Different crops provide different key challenges for the applicator:
- Waxy, hard to wet surfaces (e.g. onions, brassicas)
- Dense canopies (e.g. potatoes, tomatoes, curcurbits)
- Drift issues and windy conditions, depending on location
- Overhead irrigation interferes with applications
For many fungicides and insecticides coverage is essential to achieve good efficacy. Most chemical labels assume that 1000-1100 L per ha is somewhere around the dilute mark for mature crops e.g the Champ Dry Prill WG label rate in potatoes is 140 g/100 L or 1.55 Kg/ha (= 11 x 100 L rate). While it is not necessary to spray with such a high water rate the applicator should be aware that cutting the water rate down to let say 250 L/ha compromises coverage.
Some vegetable crops have the hardest to wet surfaces. They are very water repellent and droplets have problems to adhere, and even if they adhere they may roll off. In these cases optimising the spray solution is more important than increasing the water rate. More water will simply run off more. The use of adjuvants becomes essential in these situations because they help droplets to adhere better and spread out without running off. Croplands highly recommends the use of the super spreader Du-Wett or at least a non-ionic surfactant such as Activator at 100 mL/100 L.
Air assisted sprayers such as the Horizon QM or the Bargam sprayer with air boom are excellent tools to penetrate into denser canopies. Another option is to use a TD twin cap fitted with 2 different flat fan nozzles that produce alternating FINE and COARSE spray qualities. The fine droplets swirl around and the coarser droplets have more potential to get down into the lower canopy. The aspect off applying two flat fans in a 60 degree angle to each other helps as well.
Drift and Wind
FINE droplets are easily blown away by the wind and cause chemical loss and potential drift issues. Growers who grow vegetables in windy conditions should consider using air-induction nozzles such as the flat fan agrotop TurboDrop or the hollow cone Albuz TVI. They will reduce drift by more than 95%. The big droplets can be made spreading by using the super spreader Du-Wett to achieve an even film.
Many vegetable crops, especially when grown in sandy conditions, need frequent watering. Surface active chemicals such as copper may be partly washed off. In these situations it could be of advantage to use extenders such as Bond or Designer to give formulations more resistance to wash off.