Floriculture Greenhouse Update

High night temperatures can cause mum flowering to be delayed.

Chrysanthemums 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 daylength on flowering of garden mums.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 73F. Garden mum cultivars vary in their sensitivity to heat delay.  Also 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 2 weeks of short days, during flower bud initiation. Plants subjected to high night temperatures after 3 weeks of short days showed no permanent damage and only exhibited delayed flowering. Dr. Kimberly Williams, Kansas State University explains heat delay in this short video.

Tina Smith, UMass Extension and Leanne Pundt, UConn Cooperative Extension

Fall mums will exhibit signs of wilting during extended periods of 90 plus degree temperatures. The solution may not be as easy as turning on the irrigation.Fall mums wilt when the soil is dry, but wilting will also occur in hot weather which may cause plants to be stressed, or if the roots are damage from a root disease such as Pythium, even if the soil is saturated with water. When the roots stop functioning normally the plants will show signs of stress by wilting.

Keep in mind fall mums can survive excess amounts of fertilizer and resulting soluble salts when temperatures are normal and soil moisture is maintained. Problems occur when the growing medium is dry and the salts become more concentrated, resulting in root damage. The plants will react first by wilting and than collapsing.

Take precautions to avoid overwater garden mums especially during periods of hot weather like this week.  Lift the pots and check the roots periodically. If the pots feel heavy and the soil is saturated, do not irrigate, even if it is hot. However, do not allow plants to dry to wilt prior to watering.

If plants are wilting on a regular basis and excess amounts of fertilizer have been used, the roots maybe damaged and root disease will occur. Check the plant roots, especially with slower growing varieties. The roots tell a lot about a plants health, often before the top growth shows symptoms.

Paul Lopes, Tina SmithUniversity of Massachusetts Extension

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Fall mums will exhibit signs of wilting during extended periods of 90 plus degree temperatures. The solution may not be as easy as turning on the irrigation.

Fall mums wilt when the soil is dry, but wilting will also occur in hot weather when the soil is saturated with water, and/or if the roots are damage from a root disease such as pythium. When the roots stop functioning normally the plants will show signs of stress.

Keep in mind fall mums can survive excess amounts of fertilizer and resulting soluble salts when temperatures are normal and soil moisture is maintained. Problems occur when the growing medium is dry and the salts become more concentrated, resulting in root damage. The plants will react first by wilting and than collapsing.

Take precautions to avoid overwater garden mums especially during periods of hot weather like this week.  Lift the pots and check the roots periodically. If the pots feel heavy and the soil is saturated, do not irrigate, even if it is hot. However, do not allow plants to dry to wilt prior to watering. If plants are allowed to wilt on a regular basis when controlled release fertilizer is used, the roots may burn and root disease will occur. Check the plant roots, especially slower growing varieties. The roots tell a lot about plant health, many times before the top growth shows symptoms.

Mum cuttings are arriving at some growers. Begin the season by reviewing your fertilizer program and teaching new employees to recognize Chrysanthemum white rust symptoms.

Mums are heavy feeders during the first few weeks. Growers use a variety of ways to fertilize mums. Some growers use 100% water soluble fertilizer through a drip system, some use 100% controlled-release fertilizer and some use a combination of water soluble and controlled-release. Regardless of the program you use, start plants off right and prevent premature buds by:

Using moistened soil when potting up plants, then water-in freshly planted cuttings with a fertilizer solution. Many growers are successfully using 200 to 300 ppm of 20-20-20 immediately after planting. The cuttings establish faster and grow more rapidly.

Do not stress the young plants during their first 4 to 5 weeks of growth, and especially during the first 10 days of the crop or plants will develop buds prematurely and plants will be short. Keep plants moist, well fertilized and properly spaced.

Also check plant roots regularly to monitor plant health.

To encourage soft growth that branches freely, many growers use 250-300 ppm 20-20-20 or a fertilizer that is at least 60% ammonical nitrogen as a constant feed during the first 2-3 weeks for all fertilizer programs. Then, growers using 100% water soluble fertilizer throughout the season, switch to 200-250 ppm 20-10-20 constant feed for 3-4 applications and then rotate to a calcium nitrate based fertilizer such as 15-0-15 for 1 application, then repeat. The 20-10-20 contains less ammonical nitrogen. Once plants start to show color, fertilizer is reduced to 100 ppm constant feed.

If using controlled-release fertilizer, keep in mind that the rate of release is affected by its formulation (rate of release), soil temperature and frequency of irrigation. Most formulations release at temperatures of 70°F or above, therefore during cool temperatures, fertilizer is going to be slow to release. We often have cool temperatures in June when plants need the most fertilizer. This is the reason liquid feed becomes important, to get plants growing and create vegetative growth.

Garden mums initiate flower buds easily and develop rapidly if plants are stressed in any way. If terminal flower buds are observed when cuttings arrive, plants should still perform satisfactorily. When cuttings with terminal flower buds are planted, they should be pinched hard (allow 4-5 leaves to remain) when they are turgid (4-5 days after planting). This will force out lower breaks which tend to be more vegetative. If both terminal and lateral buds have developed when cuttings arrive, it is best not to plant them, as they most likely will not perform satisfactorily.

Tina Smith, University of Massachusetts

For more information see:

Fact Sheet: Garden Mums for Fall Sales. University of MassachusettsFact Sheet 2008: Chrysanthemum White Rust. University of Massachusetts.Grolink: Belgian Mum Cultural Information Fact Sheet. Garden Mums from Cell Paks. Griffin Greenhouse Supply Company.

Weather related problems were observed over this past week. Paper thin brown spots - sunscald (many crops) caused by sun and wind, wilted new growth (basil) caused by chilling injury and silver color foliage (bacopa) were just a few of the symptoms observed. Shade perennials placed in full sun in both retail and grower locations resulted in sunburned foliage. Continue to watch weather reports over the next week. Cover plants at night, protect plants from the wind. Gradually expose plants grown in the greenhouse to cool temperatures.

Late season thrips and Impatiens necrotic spot virus were observed on plants this week.

Many growers used biological control for aphids and other pests this season. There has been confusion over identification of aphid mummies versus healthy aphids at retail locations. See photos of black aphid mummies and brown aphid mummies, many on a leaf.

Monitor for Rhizoctonia web blight on impatiens, herbs and other plants encouraged by dense canopies, closely spaced plants and humid conditions. Rhizoctonia is more commonly known as a fungus that causes root rot diseases.  It may grow up from the media causing web blight during favorable environmental conditions. Stems and leaves collapse, with fine, web-like mycelium present. If you look closely, you can see the fine strands of the fungus.  If there are certain houses or locations where you have seen outbreaks of Rhizoctonia web blight, consider growing crops that form a less dense canopy in those locations.  Web blight can occur in the some locations and on the same crops year after year.   Many of the fungicides labeled for Rhizoctonia root rot may also be helpful in limiting web blight. Rhizoctonia is a natural inhabitant of the soil and can survive there indefinitely.

Leanne Pundt, University of ConnecticutTina Smith, University of Massachusetts

Many growers are reporting that mums are shorter and are flowering earlier this season. Cool temperatures,cloudy and rainy weather have been the norm this summer. Take advantage of sunny days to fertilize plants.

Premature budding Chrysanthemum flower buds initiate easily and develop rapidly, especially if plants are stressed in any way. Lack of adequate fertilizer and cool nights are causes for premature budding. When grown outdoors, we are relying on natural daylength and temperature to control the timing of the crop. Chrysanthemums are short-day plants. Both flower initiation and development of the flower buds occur more rapidly under short days than in long days. However, temperature has a greater influence than daylength on flowering of garden mums. With several cool nights in a row, garden mums can initiate many buds prematurely which results in early flowering of plants.

Short plants. Again, short plants are a result of plants setting bud too early. In chrysanthemums, flower bud initiation marks the end of vegetative growth. Garden mums initiate leaves rapidly. Cool weather early in the growing season will reduce the number of leaves formed on each shoot, thereby, resulting in plants with fewer nodes and shorter plants. Another reason for smaller, harder plants may be due to lack of nutrients. Frequent rain made it difficult to keep plants fertilized. As a result, nutrients were leached and plants stopped growing.

How growers responded. Some growers pinched buds off of plants (in July) and fertilized more often with higher rates (350 ppm) to allow plants to grow larger and flower later. This may not work for very early and early flowering varieties that are programmed to flower early.

Some growers left buds on plants and fertilized with up to 400 ppm nitrogen of 20-10-20. Some growers even included ammonium forms of nitrogen (20-20-20) in their fertilizer program. The theory being that vegetative growth would by-pass the budded growth. In some cases this has worked while for most it resulted in uneven plants with short, budded or flowering plants surrounded by some tall growth, but not enough to fill out the plant, creating two-tiered plants. Growers also reported that the plant’s response has varied according to the variety.

At this time, mums should receive constant feed of 300 ppm nitrogen from fertilizers like 20-10-20 to promote vegetative growth. Reapply up to 400 ppm after each rain to keep sufficient nutrient levels. Note that root health should be monitored.  Diseased roots will not take up fertilizer.

Final note: Some growers have asked about using Fascination [a cocktail of two plant hormones, gibberellic acid (GA4+7) and benzyladenine (BA) in equalproportions] to increase plant height. Fascination increases height by stretching the distance between the leaves. Trials using Fascination on poinsettias have shown that it will stretch soft tissue about an inch per application. Response is quick, within one week of application you will know how much additional growth the treatment produced.  Application can be repeated as needed but results are best when shoot growth is still soft and several of the upper internodes have not yet expanded. Once stems harden they will be less responsive to treatment and late treatments may just cause the flower buds to stretch above the foliage. Trials using Fascination on garden mums has been minimal at this time but preliminary results show increased stem length with a 10ppm spray application. 

For more information (and photo) of Fascination on mums: GroLink July Newsletter

Tina Smith, University of Massachusetts Rich McAvoy, University of Connecticut

Tomato seedlings are for the most part, easy to grow, but every so often a problem will arise. Distorted leaves and aborted growing tips can often be explained away with evidence of herbicide use in or nearby a greenhouse or a virus originating from the seed. In this case excess fertilizing is more likely the cause.

The problem developed in a growers greenhouse affecting 90% of the crop. The tomato seedlings were in 12 inch patio pots, 3 plants in each pot. A soil test was completed on the soilless mix and the results indicated soluble salt levels of 3.04 mS/cm, an ammonium nitrogen level of 46 ppm and a sodium level of 101.2 ppm.

Tomatoes in general can tolerate high salts and high ammonium levels but tomato seedling 3 to 4 weeks old can be damaged. Leaching the soil with clear water and changing the fertilizer to a higher nitrate form is the recommendation but the plants will need to be watched to see if the new growth will return to normal.

Photo: Tomato Seedling with Symptoms

Paul Lopes, University of Massachusetts