Azoxystrobin vs Propiconazole: One Misses Dollar Spot

These two products sit next to each other, cost within a few dollars of each other, and between them cover almost every fungal disease a home lawn gets. They are still not interchangeable, and the reason is one disease that appears on one label and not the other.

The Gap That Decides It

Virginia Tech’s turfgrass pathologist puts it in one sentence, and it is the single most useful sentence in this whole subject:

“Azoxystrobin is a phenomenal active ingredient for suppressing brown patch, and quite a few other diseases, but it essentially has no activity against dollar spot.”

Propiconazole gets a different character reference from the same page — “a good general fungicide that covers many diseases” — with the trade-off named too: less longevity than azoxystrobin on brown patch.

So the two are not ranked, they are shaped differently:

Those two numbers are Clemson’s, and they turn “longer” into something you can budget with:

“In general, azoxystrobin or pyraclostrobin will control diseases of lawns for 28 days. The other four fungicides will control the diseases for 14 days.”

Twice the interval means half the applications across a season — which frequently reverses the cost comparison people make at the shelf, where azoxystrobin looks like the expensive one. Price the season, not the bottle.

Clemson also settles the dollar spot question from the other direction. Their list of what works reads “fungicides that give good control of dollar spot should contain propiconazole, azoxystrobin with propiconazole, or triadimefon.” Azoxystrobin appears only in combination — never on its own. Two programmes, one saying it has no activity and the other declining to list it alone, is as close to settled as this gets.

Which means the identification has to come first, and it is not a close call visually: brown patch produces roughly circular patches from six inches to several feet across, while dollar spot produces small straw-coloured spots about the size of a coin. If you cannot tell which you are looking at, lawn fungus identification sorts them by patch size, blade lesion and season before you spend anything.

What Each Label Actually Carries

We read both registrations on EPA’s label system rather than trusting either box, and the difference is exactly where Virginia Tech says it is.

The azoxystrobin granular is registered as Lawn Fungus Granular — DiseaseEx is a brand name sitting on that registration — at 0.31% azoxystrobin. Its label lists nineteen diseases, including anthracnose, brown patch, cool weather brown patch, fusarium patch, gray leaf spot, leaf rust, necrotic ring spot, pink patch, powdery mildew, pythium blight, red thread, rhizoctonia large patch, snow mold, spring dead spot, stem rust, summer patch, take-all patch, yellow patch and zoysia patch.

The word “dollar” does not appear anywhere on it.

That is worth pausing on, because it is the case where two independent kinds of evidence agree. A missing entry on a label can mean many things — a registrant who never sought the use, a narrowed distributor label, a bag printing a short version of a longer master label. Here it means what Virginia Tech says it means. When the label omission and the pathologist agree, the omission is describing the biology.

What each label actually covers

19 vs 8 diseases on the labels

Azoxystrobin — 0.31% granularPropiconazole — 2.42% concentrate

Only Azoxystrobin

11

• cool weather brown patch
• fusarium patch
• gray leaf spot
• necrotic ring spot
• pink patch
• pythium blight
• snow mold
• spring dead spot
• take-all patch
• yellow patch
• zoysia patch

Both labels

7

• anthracnose
• brown patch
• large patch
• powdery mildew
• red thread
• rust
• summer patch

Only Propiconazole

1

• dollar spot

One caveat on this registration. It is a master label carrying bracketed optional text, which means a specific retail bag can legally print a shorter disease list than the registration allows. If a disease matters to your purchase, read the bag in your hands rather than our list of nineteen — that is the general habit how to read a pesticide label argues for, and a master label is the clearest case for it.

The propiconazole concentrate is registered as BTF Concentrate at 2.42% propiconazole. Dollar spot appears on it nine times, alongside anthracnose, brown patch, large patch, powdery mildew, red thread, rust and summer patch. This is the reason our dollar spot page cards this product rather than the granular — not a preference, a label.

And check the form before you buy. The same registrant also holds a 0.51% propiconazole granular under a separate registration number. Same active, different product, different rate — so “propiconazole in a bag” is not the product reviewed here, and matching the registration number rather than the active is how you tell.

A third bottle that is not a third option

Myclobutanil is the other DMI a homeowner can buy, and its label is unusually candid about what that means. Atticus Gravex 20 EW states that it “belongs to the sterol demethylation inhibitor (DMI) class of fungicides and is classified as a Group 3 fungicide”, and then instructs that after two consecutive applications of it, “another myclobutanil product, or another DMI”, you rotate to something with a different mode of action.

Propiconazole is a DMI. So myclobutanil and propiconazole are the same group, and alternating those two bottles is not alternating anything. The rotation partner for either of them is the azoxystrobin granular, which is Group 11.

And a bag with both in it

They are also sold pre-mixed. Quali-Pro’s Strobe Pro G is azoxystrobin 0.31% plus propiconazole 0.75% in one granular, with residential lawns on the label — one pass instead of deciding which disease you have.

Before treating that as the obvious answer, read what its own label says about resistance. It notes the bag “contains both a Group 11/Azoxystrobin and Group 3/Propiconazole fungicide”, that “a gradual or total loss of pest control may occur over time if these fungicide are used repeatedly”, and instructs you to rotate with different groups.

A pre-mix is not a rotation. Alternating two separate products rests one group while the other works; using a combination every time pressures both at once. The convenience is real — the resistance arithmetic is worse than owning the two products separately and taking turns.

Why You Might Own Both

The strongest argument for buying both is not coverage. It is that using one of them twice is how you stop it working.

NC State is direct about the speed of the problem on the disease where it matters most:

“The fungus that causes dollar spot develops resistance to fungicides very quickly.”

And the instruction that follows from it:

“rotate among fungicide classes after each application” … “tank-mix systemic fungicides with a contact fungicide”

Azoxystrobin and propiconazole belong to different fungicide classes, which is precisely what makes them a usable rotation pair — one application from each rather than two from either.

But note the limit of that pairing here. A rotation only rotates for the diseases both products control. On dollar spot the azoxystrobin half contributes essentially nothing, so alternating them is not a dollar spot rotation — it is one effective application followed by one wasted one. Virginia Tech’s answer for that case is to combine active ingredients within a single product instead: “If dollar spot is a concern of the homeowner, it may be best to combine multiple active ingredients to ensure suppression.” Neither of the two products here is such a combination, and we would rather say so than imply a rotation solves it.

The cultural half is not filler either. On every one of these diseases the watering schedule, the mowing height and the nitrogen timing change how much disease pressure the fungicide is being asked to absorb — brown patch treatment covers that side for the disease most homeowners are actually looking at.

Which One to Buy

One disease where UF/IFAS names the class before the product is gray leaf spot — strobilurins first, propiconazole as the homeowner option, which makes it the clearest case for owning both.

Buy the azoxystrobin granular if the patches are big. Brown patch, large patch, gray leaf spot, red thread, snow mold — a long list, the longer interval between applications, and a spreader you probably already own. Just do not expect it to touch dollar spot.

Buy the propiconazole concentrate if the spots are small. Coin-sized, straw-coloured, often with an hourglass lesion on the blade. It is also the broader of the two by reputation, and the sprayed form puts the active on the leaf where these diseases live.

Buy both if you expect to treat more than once, and alternate them rather than repeating either — with the honest caveat above that this is a rotation for the diseases they share, not for dollar spot.

Buy neither until you have identified the disease. More than half the fungicide sold for home lawns is applied to drought stress, dog urine or insect damage. That is the entire reason lawn fungus identification exists, and it costs nothing.

One case where the active ingredient choice is not a preference but a mismatch: Pythium is a water mold rather than a true fungus, so products bought for brown patch are not automatically active on it. Lawn disease after flooding covers when that distinction decides the purchase.

The Short Version

One gap decides it. Virginia Tech: azoxystrobin “essentially has no activity against dollar spot.” The label we read agrees — nineteen diseases, and “dollar” is not one of them.

Azoxystrobin lasts longer on brown patch. Propiconazole covers more ground overall and carries dollar spot.

Rotate if you treat twice, because NC State says the dollar spot fungus develops resistance very quickly — but understand that a rotation only rotates for diseases both products control.

Read the bag, not our list. The azoxystrobin registration is a master label, so a retail bag may print fewer diseases than the registration permits.

And identify first. Neither product does anything for the drought stress it gets bought for.