Manure and poor plant growth!

Manure from horses or farm livestock, is a wonderful soil conditioner and natural fertiliser.

Where is it used and subsequent plant growth is less than ideal then this might be directly linked to the manure or compost or it may be down to other co-incidental factors such as poor quality seed, unfavourable weather conditions, insect pests, disease or virus.

This site though focuses on the potential for herbicide residues that may be present in manure to subsequently affect plant growth and what sort of action one can then take to remedy the situation.

If manure is the presumed cause of poor growth then that might be because of a number of factors such as:

  • Too much manure
  • Green manure which typically contains a high component of cellulose that tends to draw in valuable soil nutrients to aid its breakdown process
  • Presence of herbicides which have previously been applied to either grazing grass or to silage or hay that has subsequently been consumed by livestock

How do you know if there is herbicide residue in your manure?

  1. Ask the supplier if there have been any other incidents of poor plant growth
  2. Check with them on its origin and whether they can be sure that no herbicide has been used in pastures where animal manure has been collected
  3. Test the manure by growing a plant sensitive to herbicide presence (broad bean is a good option). Click here to see how to perform the test (Bean Test).

Why herbicides might be found in manure?

The answer is, of course, that they shouldn't be. When a farmer uses a herbicide to control weeds in grassland and the direction on the product label is adhered to, then no manure should subsequently be produced which has a herbicide residue within it.

Occasionally, mistakes are made and manure or indeed hay or silage, that has a herbicide residue within it may leave a farm and end up causing a problem elsewhere. One such herbicide residue that has been found in gardens and allotments via manure is aminopyralid.

What is aminopyralid?

Aminopyralid is the active ingredient in the herbicide Forefront® T. This herbicide is the most effective product for lasting control and elimination of many deep-rooted perennial weeds found in grassland, including docks, thistles, buttercup, dandelions, nettles, and ragwort. It is completely safe to grass but will kill clover.

Forefront T is a product favoured by grassland farmers who have severe weed infestations of perennial weeds such as docks, thistles and ragwort. The label is clear and directs farmers to use on grazing grassland, grazed by cattle and sheep only.

If the Bean Test shows abnormal growth that is characterised by cupped leaves and fernlike growth on new shoots then Forefront T could be present and this will be a consequence of the label requirements not being followed. Signs of other kinds of damage will most likely indicate other issues such as damping off or bacteria-infected soil, etc. or another type of herbicide.

If you believe you have manure containing aminopyralid, please contact us.

Is aminopyralid safe?

Aminopyralid poses no health risk to any animal that eats treated grass, but there is enough active ingredient in the manure to cause a problem for plants that are sensitive to it, such as potatoes and legumes.

How can I resolve the situation?

If you still have manure, and you are sure it has herbicide residues then contact the supplier and ask for it to be collected.

If there is manure visible on your vegetable ground or flower beds then rake off, bag up and dispose of via a land fill site (non recyclable waste).

If manure has been dug into the ground then either:

  1. Plant vegetables or flowers that are not sensitive to aminopyralid (see list of plants to avoid below).
  2. Dig and mix the manure into the soil and ensure there is adequate moisture to speed up the breakdown process. Aminopyralid decomposes with the help of micro-organisms found in soil. Manure that has been well-rotovated into the soil and turned over regularly is safe to use on all but the most sensitive plants after 6 months. Properly incorporated manure is considered aminopyralid free after one year. Do a Bean Test to be sure.

Will all my plants be affected?

No. Only vegetables and ornamentals such as the following are susceptible to aminopyralid residues:

  • Potatoes
  • Peas, beans, and other legumes
  • Carrots and other umbelliferae
  • Tomatoes
  • Lettuce, spinach, and other compositae
  • Dahlias
  • Some species of roses

If you have planted any of these susceptible crops, but only some of them are affected, it is unlikely that aminopyralid is the cause of the damage to the crops.

 

See our Frequently Asked Questions for further informtion, or email us at UKHotline@dow.com.

For examples of plants affected by amionpyralid residues click here for photographs.