 Delay of garden mum flowering and in more extreme cases, failure of buds to develop properly (crown buds), are often associated with heat delay.Quick Tip 1Chrysanthemums are short-day plants. Both flower initiation and development of the flower buds occur more rapidly under short days than under long days. However, temperature has a greater influence than day length on flowering of garden mums. In areas where night temperatures are very warm, mum flowering is often delayed. Delay of flowering and in more extreme cases, failure of buds to develop properly (crown buds), are often associated with heat delay. Heat delay occurs when night temperatures are greater than 73°F. Research at Kansas State University has shown that plants are more sensitive to heat delay when plants are subjected to high night temperatures during the first two weeks of short days, during flower bud initiation. Plants subjected to high night temperatures after three weeks of short days showed no permanent damage and only exhibited delayed flowering.  Growers using biological controls should know the pesticide history of their starter plants.Quick Tip 2Growers planning to use biological control for pest management on poinsettias, should request the pesticide history of their cuttings. Last year, some growers had problems with biocontrol for whitefly due to pesticide residue on their cuttings. Pesticide residues negatively affected biocontrol agents for the first three to four weeks of the crop after arrival at the finishing growers operations. As a result, biocontrol agents were not able to establish on the first generation of whitefly. Fungus gnats are a common problem at rooting stage or at planting stage of rooted plants, and they can also damage older plants. Growers in Massachusetts and Connecticut have had success using the beneficial nematodes Steinernema feltiae to manage fungus gnats for spring crops this year. Growers will be using them for poinsettias and other fall crops also. Some growers used weekly applications for spring crops and reported that they also reduced their thrips populations. Unlike many traditional pesticides, beneficial nematodes have no restricted entry interval (REI) or possibility that the fungus gnats will develop resistance. Beneficial nematodes are living organisms, so there are precautions that need to followed for their successful use. Nematodes can be applied using a sprayer, injector, hose end sprayer or even a watering can. If using an injector, set the dilution to 1:100. Remove all filters or screens (50 mesh or finer) in any spray lines so that the nematodes can pass through undamaged and spray pressure should be kept below 300 pounds per square inch. Although nematodes are applied in water, they are not aquatic and need adequate aeration while in tank solutions and during application. Many growers use a small battery powered submersible pump to keep the solution aerated and to keep the nematodes from settling on the bottom.  Care needs to be taken when controlling weeds around greenhouses with herbicides.Photo courtesy of Conrad Fafard Inc.Quick Tip 3While it is good practice to control weeds in and around greenhouses to manage potential incoming greenhouse pests, always use care when using herbicides around greenhouses. Auxin-type herbicides such as lawn or brush-killing herbicides containing 2,4-D, dicamba and MCPP are very volatile. Vapors can easily buildup within an enclosed greenhouse and injure desirable plants. Auxin-type herbicides can cause very distinguishable injury symptoms that include cupping and strapping of plant foliage. Always be sure the chosen herbicide is labeled for use in the greenhouse and carefully follow label instructions and precautions. Before spraying weeds around the greenhouse with any herbicide, close windows and vents to prevent spray drift from entering the greenhouse. Avoid using volatile herbicides that can easily enter the greenhouse ventilation system. Use a dedicated sprayer that is clearly labeled for herbicide use only. I am aware of a grower who used a brush killer on the perimeter of an empty, uncovered greenhouse in the fall and covered the greenhouse several weeks later. The greenhouse remained empty until spring. During the spring growing season, susceptible tomato plants exhibited herbicide injury along the benches of the outside walls, where the herbicide had drifted into the greenhouse before it was re-covered.  Now is a good time to visit trial gardens in your region to see how plants performed. Photo courtesy of University of GeorgiaQuick Tip 4This is a good time to take advantage of display and trial gardens to see how plants perform in your region. Trials measure how well a particular variety will perform in different parts of the country and evaluate new plant varieties. Display gardens offer a view of how your customers see plants. There are many types of trial and display gardens conducted by botanical gardens, arboretums, colleges, universities and cooperative extension, garden centers, plant propagators, seed companies, city civic centers and public parks. For example, there may be trial gardens exclusively for garden mums, cut flowers or seed annuals or gardens with a variety of plant material planted in containers and in landscapes. There is a difference between a trial garden and a display garden. A trial garden is a test site that conducts side-by-side comparison trials. Plants in a trial garden are methodically grown and evaluated. A display garden is located in a public place, open to the public. A display garden is not required to evaluate and report the performance although some display gardens do. A good place to begin to find gardens is through the All-America Selections website, your state university extension system or Google “trial gardens” + your state. |
Explore the August 2011 Issue
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