Beware of rotational restrictions when choosing herbicides for weed control

When using herbicides for weed control on a diverse crop rotation, keep in mind that herbicide carryover can injure subsequent vegetable crops.

Crop rotation is a powerful tool for risk management on the farm. Crop rotation impacts soil fertility and can be instrumental in limiting problem pests such as insects, diseases and weeds. While some crops in your rotation may yield lower profit margins than others, it is important to remember that crop rotation is a multi-year investment that can increase your productivity over the long haul.

When designing a crop rotation plan on your farm, multiple components enter the equation. Crop selection, their sequence in the rotation, the botanical family of the crop (Table 1) and the pest problems observed in the fields in previous growing seasons all factor into designing a rotation.

Table 1. Vegetable crops and their taxonomical families.

Family

Also known as

Vegetable crops 

Alliaceae

Allium

Onion
Green onion
Garlic
Leeks

Chenopodiaceae

Goosefoot family

Beets
Swiss chard
Spinach

Apiaceae

Umbelliferae

Celery
Carrot
Celeriac
Parsnip
Parsley
Cilantro

Brassicaceae

Cole crops/crucifers

Cabbage
Cauliflower
Broccoli
Turnip
Rutabaga
Kale
Radish
Horseradish
Brussels
Sprouts
Collard and mustard greens

Cucurbitaceae

Cucurbits

Cucumber
Pumpkin
Watermelon
Cantaloupe
Squash
Zucchini

Fabaceae

Legumes

Green beans
Lima beans
Wax beans
Peas

Solanaceae

Nightshade family

Tomato
Potato
Pepper
Eggplant
Tomatillo

When planning your rotation, it is very important to have accurate records of the weed species causing problems in specific fields. For information on identifying weeds, visit MSU’s Identifying weeds in field crops webpage, or purchase the handy IPM Pocket Guide for Weed Identification in Field Crops from the online Michigan State University Extension Bookstore. One of the most important weed control principles is to understand weed lifecycles and how weeds are genetically related to the crop (e.g., do they belong to the same family?). When a weed and a crop belong to the same family, it is difficult to achieve acceptable weed control because effective herbicides can injure the weeds and the crop. This is why it is common for growers to struggle to control weeds from the nightshade family in tomatoes and peppers; all these plants belong to the family Solanaceae.

The herbicide active ingredient halosulfuron (Sandea, Table 2) is a herbicide labeled in sweet corn that is effective in controlling nutsedge applied post-emergence. However, this particular herbicide has rotational restrictions that range from eight to 36 months before vegetables and other crops can be planted. For example, 15 to 18 month are needed before cole crops can be planted, and eight to 12 months before any solanaceous crops can be planted (review the herbicide Sandea label at CDMS Labels/MSDS for rotational restrictions by specific crop).

In cases where the rotation comprises mainly vegetables staggered throughout the growing season, herbicide application should be carefully considered. Notice that most herbicides have rotational restrictions on their labels. Table 2 lists some herbicides with rotational restrictions. For more information, check the Michigan State University Extension bulletin E-433, 2014 Weed Control Guide for Vegetable Crops, and review the specific herbicide label at CDMS Labels/MSDS.

Table 2. List of some herbicides labeled for vegetables with rotational restrictions.*

Trade name

Active ingredient

Remarks/Limitation**

Command

clomazone

Rotational restriction, small grain sensitive to carryover.

Stinger

clopyralid

10.5 to 18 months rotational restriction.

Reflex

fomesafen

Rotational restrictions (most vegetables 18-month rotational restriction); use once in two years.

Option

foramsulfuron

60-day rotational restriction most crops.

Sandea or Permit

halosulfuron

Rotational restriction, carryover can injure beets.

Pursuit

imazethapyr

Label rotational restrictions, may cause carryover injuring peas.

Callisto

mesotrione

Label rotational restrictions (most vegetables 18-month rotational restriction).

Dual Magnum

s-metolachlor

Wait five days after planting barley.

Sinbar

terbacil

Do not plant any crop other than asparagus within two years of app.

Impact

topramezone

Most vegetables 18-month rotational restriction.

Laudis

tembotrione

18 months for most vegetables.

*The information presented in this table was summarized from the 2014 Weed Control Guide for Vegetable Crops, MSU Extension Bulletin E-433.
**Read the label and follow all instructions closely. The use of a pesticide in a manner not consistent with the label can lead to the injury of crops, humans, animals and the environment, and can also lead to civil or criminal fines or condemnation of the crop. Pesticides are good management tools for the control of pests on crops, but only when they are used in a safe, effective and prudent manner according to the label.

If you grow field or row crops and rotate with vegetables, review MSU Extension specialist Christy Sprague’s table summarizing herbicide crop rotation restrictions in the 2014 Weed Control Guide for Field Crops bulletin. Dry conditions affect carryover as Sprague discussed in her 2012 article “Dry conditions will likely impact herbicide carryover to rotational crops.”

If you want to learn more about more about soil health, crop rotation and weed management in diverse vegetable rotations, consider attending the third annual Integrated Pest Management (IPM) Academy Feb. 18-19, 2014, in Okemos, Mich., just outside of East Lansing, Mich. The Academy includes morning sessions on Soil Health: What is it, Why is it Important and How Can It Be Managed and an afternoon session devoted to Managing Pests in Diverse Vegetable Rotations.

To register for the 2014 IPM Academy, visit http://bit.ly/ipm-academy14 and download the event flyer to view the full agenda.

Print copies of the bulletins mentioned in this article can be found with a search at the MSU Extension Bookstore website and obtained through your local county MSU Extension office or at the Integrated Pest Management Academy bulletin table.

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