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Ministry of Agriculture, Food and Rural Affairs

Critical Weed-Free Period

The goal in managing weeds is to maximize yields - by suppressing weed competition during critical periods of crop development.

This concept is called the Critical Weed-Free Period, when it is most important to control weeds to prevent competition with crops. It is important to understand these facts about the Critical Weed-Free Period:

Critical Weed-free Period for Horticultural Crops
Crop Critical Weed-free Period
Apples, new plantings During May and June
Apples, bearing Budbreak until 30 days after bloom
Beets First 2- 4 weeds after planting
Cabbage, early First 3 weeks after planting
Carrots First 3- 6 weeks after emergence
Corn 3rd to 8th leaf
Cucumbers, pickling First 4 weeks after seeding
Lettuce First 3 weeks after planting
Onions The whole season
Potatoes First 4 weeks after planting
Squash Early plantings compete better
Strawberries, new During May and June
Tomatoes, fresh First 36 days after transplanting

There are other valid reasons to control weeds outside of these critical periods such as: attractiveness for PYO customers, harvest efficiency, and reduction of weed seed banks. However, controlling weeds outside of the critical weed-free period will NOT increase yields.