Do the math: Tank mix combinations

Maintaining high-quality golf course turf during the growing season requires considerable inputs. We add nutrients to promote an ideal growth rate and maintain a healthy turf. We apply synthetic or biological pesticides to manage pests, and we use products like wetting agents to enhance the role of soil in maintaining healthy plants. The turf market offers numerous products that may help provide turf health.

We often tank mix combinations of these products in a 150- to 300-gallon sprayer and apply at approximately 44 to 88 gallons per acre. The reasons for tank mixing range from efficiency (superintendents don’t want to be spraying more than they have to) to mandates (golf course spraying is limited to when the course is closed). How many products are often tank mixed together? The number varies widely. The most that I have heard is 26, but it’s not uncommon to hear eight to 12 products.

Your tank mixes generally have developed over time based on suggestions and recommendations from others to trial and error, with the result being a desirable spray. But what happens when — let’s say during summer stress — your spray causes turf injury? That’s when the finger pointing begins. “It must have been such and such product,” you think. But how do you really know if it was one product, or if it was the interaction of products under the given conditions that caused the injury?

Let’s have some fun and look at a hypothetical scenario to answer our question.

We tank mix 10 products together and spray our fairway (or greens). We notice turf injury a day or two later. Given that it’s the middle of summer and the turf is under stress, we assume (rightly or wrongly) that what we sprayed caused the damage. We make this assumption because we saw no damage when we previously used this tank mix. We need to know specifically what product or products caused the damage so as to minimize the chances of injury occurring again. So we approach a turfgrass researcher to conduct a study to determine the cause.

To set up this study the researcher looks at all combinations of products mixed in the tank, which would be the treatments. In other words, the number of treatments would be all possible combinations: 10 x 9 x 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1 or 3,628,800 treatments. The researcher replicates each treatment at least three times, which leaves us with 10,886,400 plots. If each plot were 3 feet by 5 feet (15 square feet), we would need approximately 3,749 acres of fairway turf. If the researcher assumes that 25 acres of fairway exist on a golf course, he/she needs 150 golf courses to do the study.

Our researcher most likely makes treatments with a carbon dioxide (CO2) backpack sprayer consisting of a CO2 canister that pressurizes a 2-liter bottle containing the treatment. The researcher needs 7,257,600 liters of water (3,628,800 treatments times 2), or 1,917,255 gallons of water, to fill the 2-liter bottles. For perspective, a tanker truck that pulls into a filling station contains 9,000 gallons of gasoline. I wonder how long it would take just to fill the 2-liter bottles, or if it be possible to apply all the treatments in one day? I don’t know, but my brain just exploded.

Actually, the above scenario is a pretty simple one. We do not account for formulation changes that may occur between patented or off-patent products, special formulations or combinations of actives within a product.

Under extreme summer stress, I recommend reducing the number of products you mix in a single spray tank to reduce the likelihood of injury. For example, if turf injury occurs with a three-product tank mix, the total number of treatments needed to identify the problem would be 6 (3 x 2 x 1 = 6 treatments). I think I could do that.