Using Casoron Herbicide for Apples

What it is:

Casoron is a granular herbicide that is registered for use on apples, other fruit trees and vineyards. It is also registered on raspberries, cranberries, blueberries, saskatoons, and woody nursery stock (both container and field grown. It controls a broad-spectrum of weeds, including many annual grasses and broadleaf weeds, plus some perennial weeds* like Canada thistle, quackgrass, bindweed, dandelion, horsetail, yellow nut sedge, sow thistle, and vetch. (*Perennial weeds usually require higher rates and late fall applications).

How it works:

When Casoron is applied to cool moist soil, the active ingredient, dichlobenil, is released as a vapour, and is absorbed in the top 5 centimeters of soil. A herbicidal barrier forms in the top layer of soil, and kills the growing points of roots and shoots that try to grow through it. Annual weeds are killed as they germinate. Some perennial weeds are killed as they emerge. Crop safety is achieved when the crop roots grow below the vapour barrier.

When to apply:

Casoron is very volatile. It should be applied when air temperatures are below 10C, when soil is moist, but before it is frozen or snow covered. The ideal timing is usually sometime between November 15 and December 15, although occasionally ideal conditions in orchards may occur in March or early April . If Casoron is applied when soil or air is warm, much of the herbicide can be lost through volatilization.

Casoron can also be applied 4 weeks after new plantings, but you must consider if soil conditions are cool and moist enough. In all cases, Casoron should be applied to weed-free soil or, in the fall, before annuals germinate. Casoron will not control germinated weeds.

How much to use:

The recommended rate of Casoron refers to the area actually treated with herbicide. Remember that only a portion of your orchard (weed-free strips under the tree) will be treated with Casoron, which often makes the treatment more cost effective.

A range of rates is recommended on the label. The higher rate is for perennial weeds, and for higher organic matter soils. If irrigation is used shortly after application (eg. if soil conditions are dry, or for new plantings in early summer), use the lower rates to avoid crop injury.

How to apply:

Uniform application of the Casoron granules is important. There are a number of herbicide applicators available for spreading granular products. These can range in price from $15 to a few thousand dollars.

For a small acreage, growers can choose a hand-held applicator that is gravity fed. A Webfoot applicator holds about 3 kilograms, and retails for $15-20. Application rates of 0.1-0.2 hectares/hour are possible.

There are some backpack granular applicators with motorized fans available for slightly larger fields. They hold 4 to 6 kilograms of product, and require the operator to hold the hose that directs the granules under the plants. These applicators retail for about $300-400.

The challenge has been to find larger equipment that can efficiently and uniformly apply Casoron for larger fields. Granular products like Casoron are generally applied with either side or rear-mounted applicators like Herd or Gandy spreaders.

One custom applicator in southwestern Ontario has mounted a modified Gandy applicator on an all-terrain vehicle. His innovation has been using a fan to spread the granules under the plants. After doing custom work for several years, he has found that the best pattern was achieved by driving on each side of the row, applying half of the recommended rate each time. Custom rates with his applicator costs $35-40/hour. They are able to treat about 10 to 12 acres/day, covering a 4 foot band on 12 foot rows.

How much does it cost:

The recommended retail cost of Casoron is about $810-1285/ treated hectare (about $325-515/treated acre). Although this is more expensive than other herbicides, Casoron has a proven track record when applied under the correct conditions. As well, regular use of Casoron suppresses many perennial weeds that tend to creep into orchards as they mature. The cost of hand weeding or lost cropping due to the competition of weed escapes should be considered when comparing Casoron to other options.