How late in the fall can one go when applying a postemergent herbicide for broadleaf weeds? As long as the broadleaf weeds are photosynthesizing and appear green, a postemergent product can be applied. These products work faster when the plants are actively growing, these herbicides will still work. The chances are that you may not even see any effects on the weeds this year but over the winter they will die. If applying a postemergent herbicide try applying on dry sunny day when temperatures are warm (greater than 50 degrees Fahrenheit). If you have problems with winter annual broadleaf weeds like common chickweed, a late application of a broadleaf herbicide. The justification for this application is that these winter annuals are normally late germinators in the fall.
To Cover or Not to Cover
Contributor: Paul Pilon
To help protect and insulate containerized plants, such as perennials or woody ornamentals, many growers cover their crops during the winter months using various materials such as thermal blankets, sheets of white plastic, straw, evergreen boughs or other materials. The covering traps residual heat from the soil surface, provides buffering from low winter temperatures, and moderates the temperature of the root zone. For example, a simple thermal blanket covering dormant plants can result in temperatures of 8 to 10 degrees Fahrenheit warmer beneath the cloth as compared to the temperature of the air above the thermal blanket.
To ensure the crops are properly acclimated to cold temperatures and to improve the overall survival rate, it is important to cover the plants at the proper time. Unfortunately, the precise time to cover plants for the winter varies by geographic location and with the weather conditions each year. Since the outside temperatures may vary widely from year to year, it is not recommended to apply the coverings on a specific date each year.
The temperature of the root zone should be allowed to drop to below freezing for a short duration of time and anticipated to remain there before the plants are covered. Generally speaking, the plants should be covered as late in the season as possible, allowing them enough time to be completely acclimated to cold temperatures. Covering them too early can delay acclimation and may result in overheating, premature growth of new shoots, and may increase plant mortality.
To ensure adequate protection of the root zone, it is very important to water them thoroughly before covering them. Moist media freezes slowly and releases heat which helps to protect the roots. Dry media does not offer this type of protection and often causes significant amounts of plant injury and/or death due to desiccation. Moisture in the root zone will also increase the relative humidity under the covers, which slows down transpiration and desiccation. It is also important to apply rodent baits before covering the plants; for more information on rodent control see the Tech Note posted on 11/20/06 titled ‘Vole Patrol’.
Once growers apply the insulating covering, the crops most commonly remain sealed for the duration of the winter. With some types of coverings, such as thermal blankets, growers can easily uncover the plants during the winter months to provide ventilation, prevent diseases from occurring on evergreen varieties, monitor for diseases, and apply irrigation if necessary.
There are some disadvantages of using protective coverings. Injury often occurs to evergreen varieties or ones which have fragile stems. The size of the plant materials may restrict their use or reduce the benefit of using them. For example, tall plants like ornamental grasses or small trees may have to be laid down sideways in order to properly cover and insulate them. Rodents love the habitat created beneath the covers. Air circulation is greatly reduced which may lead to the occurrence of fungal pathogens. Temperatures may build up under the covers, which may cause the plants to de-acclimate. Despite these negatives, the advantages of covering by far outweigh the disadvantages.
Paul Pilon, Perennial Solutions Consulting. E-mail: paul@perennial-solutions.com