Removing Orchards or Vineyards? Be Aware of Herbicide Residues

Fruit growers need watch for herbicide carryover when trees or vines are pulled out. Be aware of Princep or Simazine, Karmex or Diurex, Sinbar, Casoron, Devrinol (mostly of concern for cover or cereal crops), and Lontrel (mostly of concern for vegetables and soybeans). Other soil applied herbicides (Dual Magnum, Treflan, Frontier, Sencor, Lorox, Kerb) would likely be degraded within a year.

Herbicide residues are affected by several things:

1. rate applied
2. time since application
3. soil pH
4. soil organic matter
5. soil moisture
6. how soil is managed after removal.

There are 2 tests for residues: a chemical test, or with a greenhouse bioassay. Neither test is perfect, cheap or quick. A bioassay involves taking soil samples from sprayed and unsprayed areas, and growing test crops like cucumbers and oats. At least 4-6 weeks are needed to detect injury, and results are not always conclusive.

Here's some ways to reduce herbicide residues:

• Plowing will dilute the residue through a greater volume of soil. Avoid creating a zone of concentrated herbicide by flipping the soil over completely. Adjust the plough for a good mixing action.
• Adjust soil pH to 6.0 to 7.2.
• Improve organic matter with cover crops, mulch, manure, etc.
• Avoid long-residual herbicides for one, or preferably 2 years before removal.
• Change row alignment (eg. N-S to E-W) to avoid old rows.
• Avoid high value crops in the year after removing.

A few moments to assess the risk of herbicide carryover can avoid serious damage to future crops in old orchard and vineyard sites.