Apple,
Captan used to be universally labeled for pears. Now, as I understand it, only some homeowner formulations of Captan are labeled for pears. I’m guessing the reason is due to the potential of cosmetic fruit injury of some varieties. Since homeowners have fewer choices and there is no potential for income loss (because they aren’t selling the fruit) EPA and the manufacturers probably left the old registration in place for homeowners.
I recall something similar happened w/ Pristine. When Pristine first came out, it was universally labeled for blueberries. A few years ago apparently Pristine caused some blueberry crop injury in California (due to tank mixing Pristine with some other fungicide). The end result was that BASF voluntarily pulled their registration for blueberries from California. However, Pristine is still used on tens of thousands of acres of blueberries in Michigan and in the South.
Wettable Powders (WP) and Water Dispersible Granules (WDG) are basically the same thing. WDGs are basically “pelletized” or “granulized” wettable powders. Manufacturers do this for the reason you mention (less inhalation exposure for the applicator/mixer). Feed companies do the same thing to animal feed. There are a few other benefits to pelletizing/granulizing animal feed but a big one is it cuts down on dust.
WDGs take a few moments longer to break down the granules in the water vs. WPs but the difference is hardly noticeable. I wouldn’t let that be a factor at all in determining which to purchase. Both WDGs and WPs are suspension type formulations which means they will settle out of the suspension if allowed to sit for very long. The little micro particles don’t really dissolve in the water (like table salt would). Instead they just float around.
My wand sprayer doesn’t have any agitation. I stick the wand in the tank and pull the trigger to mix up chemicals. After that, the sloshing from driving around seems to keep things mixed up pretty good. I wish my wand sprayer had agitation, but when I bought it I couldn’t justify shelling out the money for a better sprayer.
I use Captan 80 early in the season to control scab. I use it on the 35 peach trees in my backyard with my wand sprayer. Most recommendations for commercial peach orchards state it takes 250 gallons/acre for a full dilute spray for a mature peach orchard. This is the basis I use to convert acre to gallon rates for use in hydraulic wand sprayers.
In your example, 4 lbs. of Captan/acre = 64oz. of Captan/acre. Since it takes 250 gal. of spray/acre for a full dilute spray that figures 0.256 ounces of Captan per gallon of spray solution (64 ounces divided by 250 gallons). If the tank holds 25 gallons, that would equal 6.4 ounces of Captan per 25 gallons. Of course this type of conversion depends on exactly how much you wet the tree, but for my sprayer tip and the way I spray, it works pretty well for me.
Alternatively, I’ve calculated the total square footage of the canopy of the trees I’m spraying and mixed the chemical based on converting acreage to square footage (i.e. 43560 sq.ft./acre. If spraying 10000 sq ft, that’s 22.9% of an acre. At the 4 lb/acre rate, that would be 0.92 lbs, or 14.7 ounces for the area spraying).
Both methods turn out pretty close for my wand sprayer, so I use the first method (gallonage conversion) because it’s easier.