Weed inventories help you select proper herbicides

Published May 04, 2007

It’s safe to say that all nurseries and greenhouses have weed problems. If growers don’t manage weeds to some degree, they will seriously rob the ornamental plant farm of profits, quality or numbers of salable plants.

{sidebar id=67}

Best practices involve assurances of quality. Thus, best practices involve some sort of weed management program or system. There are many such programs. Most involve a heavy reliance on herbicides. There are hundreds of herbicides labeled for use in nurseries on ornamentals.

Kinds of weeds

Start by learning what kinds of weeds you have the most problems with. Unless your nursery is brand new, you’re already using a variety of herbicides for the weeds you have.

But, from my experience, I’m guessing you’ve chosen products for the wrong reasons. You need to start with the weeds you have, then go to product selection. Like any pest management situation, scout for your weeds.

When you find a weed that “breaks through” your control program, identify it or get it identified. Then look at products.

This is called making a weed inventory. Again, all nurseries will have troublesome weeds that require a weed inventory. This will help you make proper management changes.

The following table is an example of a typical wed inventory for a nursery in Michigan.

Problem weeds -- container production	Type	Characteristics
Hairy bittercress	Winter or summer annual	Produces several seed crops each season. Seeds are explosively propelled. Hard to hand weed. May be resistant to Gallery.
Common groundsel	Winter or summer annual	Many generations per season. Grows in wet areas hard to cultivate. Seed is wind dispersed. Seed will mature as plants are dying, even after the plants are pulled. Has a taproot. Herbicide resistant biotypes exist.
Inula	Summer perennial	Spreads rapidly via runners. Cultivation merely breaks up stems and increases spread. Extremely invasive. Few herbicides effective at control. A new, introduced weed. May be put on the noxious weed list by the USDA.
Common chickweed/ mouse-ear chickweed	Mainly a winter annual. Mouse ear is a perennial.	Many seeds produced. Seeds can germinate all summer. Foliage easily detached from the roots when pulled. Roots survive.
Yellow wood sorrel/oxalis	Summer perennial	Seed capsules explosively ejected. Has underground rhizomes.
Liverworts	Perennial	Common herbicides ineffective. Forms dense mat on container media surface. Hard to hand weed.
Mosses	Perennial	Common herbicides ineffective. Forms dense mat on container media surface. Hard to hand weed.
Problem weeds -- field and liner production	Type	Characteristics
Common groundsel	See above	See above.
Mares tail/Fleabane/ Horseweed	Winter or summer annual/biennial	Wind-dispersed seed. Large size makes mechanical control by cultivation difficult. Grows on edges of fields.
Yellow fieldcress	Perennial	Spreads by rhizomes. Prefers wet areas hard to cultivate.
Yellow nutsedge	Perennial	Has rhizomes for spreading. Each plant can produce many tubers (nutlets) and new plants. Cultivation spreads tubers. Resistant to most common herbicides.
Canadian thistle	Summer perennial	Spreads by wind-blown seed and creeping rhizomes. Many seeds germinate in the early fall. Large size makes cultivation difficult. Cultivation breaks up rhizomes and promotes spread. Difficult to kill with herbicides due to large size.
Velvetleaf	Summer annual	Seeds large. Seeds can remain viable for 50 years or more. Seeds can sprout from well below the soil surface. Large size makes mechanical cultivation difficult. Resistant to triazine herbicides.
Quack grass	Perennial	Has aggressively growing rhizomes. Grows in border areas and ditches.
Inula	See above	See above.
Common purslane	Summer annual	Spreads mainly by fragmented stem segments. Cannot hand cultivate without promoting spread. Most herbicides not effective unless frequently applied. Tolerates poor growing sites and drought.
Redroot pigweed	Summer annual	Herbicide resistance common. Seeds germinate over many weeks. Hard to mechanically cultivate.

Using your weed inventory

Note that the table starts the thinking about strategy for control. You must determine why you haven’t gotten good control up to this point.

Most growers will want to blame the herbicide. However, it may be the application method, the application time, the dosage (targeting) or the need for follow-up treatments. Perhaps some mechanical method, such as mowing or applying mulches is needed. You may not totally escape the need for some hand weeding or cultivation.

{sidebar id=2}

I don’t want to imply that you shouldn’t revisit your product choices. There are many new herbicides coming out each year. Work with the experts in your area about your need to change products, but do so carefully.

- Charles C. Powell

Weed inventories help you select proper herbicides

Solidago hybrida Little Lemon

November issue recap

Building trust from the inside out

Petitti Family Farms opens new Red Mill propagation facility

Q&A with Theresa Specht

Garden Center magazine returns to print in 2026 with seasonal editions

Weed inventories help you select proper herbicides

Latest from Nursery Management

More from Nursery Management

Solidago hybrida Little Lemon

November issue recap

Building trust from the inside out

Petitti Family Farms opens new Red Mill propagation facility

Q&A with Theresa Specht

Garden Center magazine returns to print in 2026 with seasonal editions