We are starting to see the result of a couple of growing seasons in which dandelions have been poorly dealt with in cropland.
A large number of calls to agronomists this spring have been about dandelions and what to do ahead of seeding. Producers are now asking what they can do about in-crop solutions.
Let’s take a step back and talk about dandelions in general.
They are long-lived perennials, which form a crown that divides to form numerous branches. Each plant can produce 50 to 175 seeds per head, and a single plant can produce up to 20,000 viable seeds. The seeds are easily blown in the wind.
Dandelions are among the toughest weeds to control in a direct seeding system. Seedlings can quickly establish with the good soil moisture conditions characteristic of low soil disturbance planting systems.
Dandelion seeds germinate on the soil surface at 10 to 20 C, usually in June or July. The seeds germinate best in full light on a bare soil surface. Seedlings quickly develop a taproot and they can have a well developed crown by fall or early spring.
They are especially troublesome in a direct seeding system. Without tillage, producers have to rely on good crop competition and the timely application of systemic herbicides.
Options are available for controlling dandelion seedlings, but mature dandelions are much harder to control. Remember, a mature dandelion didn’t get there in one season and it will probably take more than one season to control.
Farmers have four opportunities to control dandelions during the year: pre-seeding, in-crop, pre-harvest and post-harvest.
A variety of products can control dandelions, depending on the crop.
The fall is the best time to control dandelions.
Glyphosate, alone or in combination with products such as Express, Express PRO, florasulam (PrePass) or 2,4-D, will provide good control. Rates will depend on the size of the dandelion plants.
Cropping restrictions may exist for next spring, depending on the product used and when it was applied.
The spring ahead of seeding is the next best time.
Products such as glyphosate alone or in combination with Express, Express PRO, Inferno DUO or florasulam (PrePass) will provide control in good growing conditions.
Time will have to be allowed for some spring growth of the plants.
Saflufenacil (Heat) and carfentazone (Aim/Cleanstart) are also labelled for spring germinating dandelions. They add to the control of overwintered plants, but the rate of glyphosate will be the major determining factor on the success. Again, the rate required and the control will depend on the size of the dandelion plants.
Pre-harvest is the third best time.
However, dandelions seem to go through a period of dormancy that lasts from early July to the end of August. This is especially true in a dry July and August.
Pre-harvest applications seem to be more effective on dandelions if done in September. This is the exact opposite to controlling perennial sowthistle, which appears to be more effective in early August.
In-crop is the least effective timing for control.
Most products control only seedlings germinating in the spring. The only exception to this is Spectrum, which lists control of over-wintering rosettes up to 15 centimetres in diameter and suppression of larger dandelions.
Products containing clopyralid will usually do a good job on smaller dandelions.
Dicamba-containing Dyvel, Dyvel DSp and Tracker XP (Target) as well as Dichlorprop – D and Express Pack do not list dandelions on their labels, but they provide good top growth control of large dandelions.
These products will do a reasonable job on dandelions in good growing conditions like we have this year.