At a recent presentation, I was asked whether a spreader-sticker should be used with all fungicides. This question led to many other questions, some of which I could answer and some I needed to research. There were many who had the same concerns.
What is a spreadersticker? Spreader-stickers are adjuvants added to the spray mix, intended to help coverage of the product on the plant material and to slow chemical residue loss. The spreader component is a surfactant that reduces the surface tension of water. This allows the product to spread across the leaf more uniformly and allows the active ingredient to be better absorbed by the plant. You have probably seen water bead up on leaves, especially on waxy-covered leaves or leaves with many hairs. Spreaders release water surface tension so the droplets dont bead up. The sticker component increases the adhesion of spray drops to the leaf and slows loss of the chemical by rain. Many stickers are also surfactants and are marketed as spreaderstickers.
Should I add an adjuvant to my spray mix in all situations? The scientific literature suggests that testing is needed on each fungicide and spreadersticker combination. Research has shown that combinations vary in effectiveness against specific pathogens. In fact, chemical effectiveness can actually decrease with some combinations. Because of different interactions between fungicides and spreaderstickers, pesticide labels often have specific directions for types of spreader-stickers to use. In some cases, a spreadersticker is already part of the product. This is the case with Remedy, a Bonide product containing potassium bicarbonate and used to control black spot, downy mildew, powdery mildew, and a variety of other foliar diseases. The label specifically states: "Do not mix with other pesticide products or spray adjuvants." In cases such as this, adding more spreadersticker could cause some plant phytotoxicity or other unexpected problems.
Can I use a homemade spreadersticker? Weve been down this road before; and the above information should explain why this is not a good idea. There is also the question of how much to use to be effective and still avoid runoff of the product. If you are insis-tent on using your own formulation on your plants, at least try it out on a few first to determine if injury follows in the next days or weeks. Such sprays are at your own risk. Commercial applicators should be able to find many spreadersticker product options.
Where can I find spreaderstickers? Some of the home gardeners I spoke with at a recent workshop stated that they could not find a spreadersticker in local stores. Others found them readily. You may need to check a few stores and concentrate on larger garden centers to find spreaderstickers. A quick Web search recently showed that Bonide makes Turbo Spreader Sticker in 8-oz bottles. Ferti-lome produces an 8-oz SpreaderSticker, a PT SpreaderSticker, and a GL SpreaderSticker. There are many other products by other companies as well. As a take-home message, always read the directions (checking the fine print) for both the fungicide and the adjuvant label before making any chemical applications.