Picloram, Clopyralid, and Aminopyralid: The Herbicides Every Hay Buyer Must Ask About

Most herbicides used on pastures break down quickly. Three don't: picloram, clopyralid, and aminopyralid. They persist in hay for years after spraying, pass through animal digestion unchanged, and remain potent in manure for months — even in compost.

If you're buying hay, you need to ask about these three. If you garden with horse manure, you really need to ask.

What they do

These are broadleaf herbicides commonly used on pastures and hayfields to control weeds without killing the grass or legume crop. They work — and they don't break down easily. That's a feature for the farmer spraying it, but a bug for everyone downstream.

The persistence problem

After application, residues remain detectable:

• In growing hay: up to 2 growing seasons
• In baled hay: 18–36 months in storage
• In manure: 6–18 months
• In composted manure: 12–24 months
• In garden soil amended with affected compost: 1–4 years

This means a single application can affect your animals — and any garden using their manure — for years.

Health impact on horses

Direct toxicity to horses from feeding affected hay is low at typical residue levels. The bigger risks are:

• Reduced palatability. Horses may refuse affected hay.
• Manure cannot be used in gardens. Tomatoes, peppers, beans, peas, and most vegetables are killed at very low residue levels.
• Pasture death. Manure spread on your own pasture can damage clover and other legumes.

For perennial peanut hay specifically (a legume), grower fields cannot have been sprayed with these herbicides without killing the crop itself. So if a grower has produced an actively growing perennial peanut field, the grower hasn't sprayed any of these recently in that field — but they may have sprayed adjacent fields, and drift is a real concern.

What to ask your hay seller

The direct question

"Have picloram, clopyralid, or aminopyralid been applied to the fields this hay came from in the past 36 months?"

The follow-up if they say no

"Are any neighboring fields under the same management sprayed with these herbicides? Is drift possible?"

The deal-breaker

If the seller says "I'm not sure" or "I don't know what herbicides we used" — that's a deal-breaker for any serious hay buyer. Records of pasture chemical application are required by state law for licensed applicators. A grower who can't answer this question is either not licensed (red flag) or not paying attention (red flag).

Trade names to recognize

You may hear these in the field instead of the chemical names:

Any of these on a feed-store shelf or in a sprayer near hay fields you're buying from = ask more questions.

The bioassay test (if you're really concerned)

If you've bought hay and want to verify before feeding or before composting manure:

1. Take a few cups of the suspect hay or manure.
2. Plant 6 bean seeds in soil mixed 50/50 with the sample.
3. Plant 6 bean seeds in clean potting soil (control).
4. Water both equally for 14 days.

If the bean plants in the test soil show distorted leaves, twisted growth, or stunted development versus the control, residue is present. Beans are extremely sensitive — much more so than horses or goats.

What we do at McDaniel Farms

• We've never used picloram, clopyralid, or aminopyralid on any field we own or manage.
• Every partner grower signs a herbicide disclosure as part of our supply agreement (see Section 8 of our grower contract template).
• We do annual bioassay testing on first cuts each season as a check.
• If a customer reports manure damage to a garden, we replace the hay and refund.

This is non-negotiable for us. Florida horse owners shouldn't have to worry about whether their hay is going to kill their tomato garden or burn their pasture.

Order verified herbicide-free hay → or call (850) 573-0470 or (850) 573-0471 if you have questions about a load you're concerned about.