Note: It is unlikely that the 12 credit requirement will affect those who are coming up on recertification soon. This will be phased in over a period of time.
Managing Resistance to Insecticides
Insecticide resistance is a major concern for chemical control of almost all the important greenhouse
arthropod pests. A combination of factors - the biology of the pests, the intensity of chemical use in the
past and the present, aspects of the greenhouse environment, and commercial production practices - has led
to insecticide resistance problems. The following suggestions should be considered for any chemical control
program.
By: Ralph Freeman, Cornell Cooperative Extension
Trials at the Long Island Research and Extension Center showed excellent results against cabbage looper in flowering cabbage. It should also perform very well against other worm pests in this crop. Growers may also want to consider using this material for control of European corn borer in mums as spinosad has had good efficacy against this pest in other corps. Growers are urged to read the label carefully and follow all recommended use. The REI is 4 hours. Dan Gilrein at the LIHREC has tested repeat applications at high rates on ivy geraniums, Petunias, and other crops in bloom with no phytotoxicity. As with other new materials, each grower should perform a small test to verify plant safety in his or her own operation.
By: Ralph Freeman
Table of Contents
Weather
Two words could sum up our weather this year: hot and dry. Although we started the growing season in March
with above normal precipitation, that quickly changed. Winter was generally mild throughout the state, so
much so that on Long Island people felt as they skipped winter altogether. Below are some highlights of
the weather in Ithaca according to Northeast Regional Climate Center at Cornell.
March, 1999
The average for May 1st had been 50 GDD50 and this year we had only reached 27 GDD50 by May 1. We were slightly above average from mid-May on. June 1 was 310 GDD50 this year, (Average is 217 GDD50 ). On July 1 there was 825 GDD50 (Average year is 712 GDD50).
Disease and Insect Incidence
This was certainly a quiet year for leaf diseases. Our lack of rain during the critical period when primary
inoculum from most leaf pathogens is produced explains this situation. There were basically few good
infection periods this year. Delayed spore dispersal allowed more twig and foliage growth to pass through
its succulent and presumably more susceptible stage, thus lessening disease incidence.
While leaf diseases were minimal because of dry conditions, those same dry conditions caused problems as well. Drought stress caused marginal scorching, early fall color, and leaf drop on many trees throughout the state, especially maples.
There were a couple of new diseases (at least for us they were new) this growing season. They were:
Source: Branching Out, Cornell University
Table of Contents
Importance of Potassium
Potassium is the most abundant cation in the cytoplasm. Its effect on the plant's water status is well
known due to its ability to regulate the osmotic potential of the cell. Water moves from a high potential
to a low potential. If the salt concentration in the cell increases, the water potential of the cell
decreases and water will move into the cell. So, when K accumulates in a cell or tissue the reduction in
the osmotic potential causes water to move in that direction. This process aids in water uptake if K
accumulates in the xylem and reduces water loss when the K concentration increases in the leaf's mesophyll
cells.
Potassium regulates transpiration in a similar way by its effect on the osmotic potential of the guard cell (those two cells that create the stomas or pores in the leaf). Light stimulates pumping of K into guard cells which increases water uptake. When guard cells are turgid they bend in such a way that an opening is created between the two guard cells, resulting in uptake of carbon dioxide for photosynthesis and water loss through transpiration. The process is reversed in the dark which stimulates pumping of K out of the guard cells, resulting in the stomates closing.
Potassium also stabilizes the cytoplasm pH between 7 and 8 which is optimal for most enzyme reactions such as nitrate reductase. Potassium is highly coupled to metabolic activity such as starch and protein synthesis, cell extension, and photosynthesis. For optimal growth, K is needed in the 2-5% range of plant dry weight of vegetative parts, fleshy fruits, and tubers.
Sources of Potassium
The average K content of the earth's crust is about 2.3%. Most of the K is bound in primary minerals or
present in secondary clay minerals. Generally, soils rich in clay are also rich in K. While clay soils
may be rich in K, organic soils are generally low in K, in the order of 0.03%.
The main source of K for plants comes from the weathering of K containing minerals such as alkali feldspars, muscovite (K mica), biotite (Mg mica), and illite, among others. The rate and extent of release of K by weathering is dependent on its concentration and the structure of the mineral. Potassium fixation can also occur and high quantities of fertilizer K can be rendered unavailable.
Soil clay content is not only important for K release and fixation but also considerably influences K's mobility. Clay minerals differ in their selectivity. Soils rich in K specific binding sites decrease K mobility and diffusion rates. Under these conditions, leaching of K is minimal. In sandy and organic soils, leaching rates may be considerable higher suggesting that K fertilization be carried out in the spring rather than the fall or winter to prevent winter leaching.
Potassium can be divided up into three fractions: K as a structural element of soil minerals, K absorbed in exchangeable form to soil colloids such as clay minerals and organic matter, and K present in the soil solution. While the fraction of K in the soil solution makes up only a small percentage of the exchangeable fraction, it is by far the most important fraction in relation to plant supply.
Potassium Uptake and Translocation
Since potassium is needed and taken up by plant tissues at a high rate, the plant depends on an active
uptake mechanism in the roots. There is evidence that of all the essential mineral cation species, K is
the only one which can be translocated against a gradient into plant cells. Potassium in the plant is
very mobile and its main transport direction is towards the meristematic (region of high cell division)
tissues. This high mobility means potassium can be imported from the oldest leaves to these growth areas
resulting in the initial deficiency symptoms showing on the older leaves.
Deficiency Symptoms
Potassium deficiency doesn't show up immediately in visible symptoms. Plant metabolism changes include
reduced growth rate of the cambium, accumulation of sugars, decrease in starch, and accumulation of soluble
nitrogen compounds. Since potassium plays a major role in plant water relations, deficiency results in
decreased turgor and reduced resistance to water stress. Therefore, resistance to drought is poor.
Affected plants are more susceptible to frost injury, ripening disorders and tuber quality as well as fungal
attack and saline conditions. Depending on the severity of the deficiency and light levels, older deficient
leaves become chlorotic and necrotic beginning in the margins and leaf tips.
When plants are deficient, increasing K levels to roots will easily increase the K concentration of various organs.
Potassium Fertilization
Potassium can be applied as part of a complete fertilizer or in the form of a compound. This nutrient is
the third number on a fertilizer bag and is expressed as percent K20. Potassium chloride (KC1), better
known as muriate of potash is the most widely used and cheapest K fertilizer. Other K sources include
potassium sulfate (K2SO4 . 43% K), potassium nitrate (KNO3. 37% K and 13% N), and potassium magnesium
sulfate (K2SO4 and MgSO4. 18% K and 11% Mg). Wood ashes and manure are two organic sources that are good
K sources.
Potassium chloride breaks down to K and C1 ions in the soil solution. Chlorogpytic species, plants sensitive to C1, such as grapes, fruit trees, cotton, sugar cane, and potatoes can be fertilized with one of the other types of K sources such as K2SO4. Potassium nitrate also contributes nitrogen while situations requiring both K and Mg can be fertilized with potassium magnesium sulfate.
Like phosphorous, K is expressed as the oxide form (K2) on a fertilizer analysis. Be sure to carefully read soil test analysis and recommendations to determine whether K is expressed in the elemental or oxide form. To convert from one to the other, use the following formulas: K x 1.2 = K20; K20 x 0.83 = K.
Potassium fertilizers are usually broadcast and only on soils with a low level of K or high K fixation. Fine textured soils which do not easily leach K may be deficient in the lower soil levels with deep rooted crops. Where K deficiency is suspected and the upper soil layer contains adequate K, sampling the lower level is advised. Deep application would be necessary to incorporate the K where the deficiency exists.
High K losses due to leaching occur only on sandy soils, organic soils and certain clay mineral soils. Treat these soils just before planting to reduce losses during excessive rainy periods. For some situations, split applications will provide more efficient use of the fertilizer from a plant and economic standpoint.
Source Long Island Horticulture News
By: Scott Clark, Cornell Cooperative Extension
Place plants in the greenhouse when the earliest bud is swollen ("puffy") and just ready to crack open. Treatment for Botrytis may be necessary. Keep the growing mix moist at all times.
Proper sampling is extremely important in obtaining an accurate diagnosis. When collecting a sample for submission, be sure to include intact plants and provide a good amount of plant material. A sample that contains root, crown, and leaf tissue enables the diagnostician to develop a complete picture of the problem during the analysis. Using a cup cutter to collect samples provides the diagnostician with a nice sized sample with which to work. Always wrap the sample in a paper bag and package it in a sturdy box. Plastic packaging material may cause the sample to heat up in transit and it often increases the humidity, promoting the growth of other organisms. It is important to collect the sample prior to any pesticide applications. This point is extremely important. Once pesticides have been applied it may be difficult to obtain an accurate diagnosis. Collect the sample from an area that has early symptoms of the problem the problem. Areas that are completely dead often contain a number of secondary organisms that could complicate the detection of the primary pathogen.
Nematodes are becoming increasingly important as turfgrass pathogens. These pathogens are microscopic worms that feed on the root systems of turfgrass plants. The best time of year for nematode analysis is during the active growing season. A minimum of 6 soil samples, approximately 1" in diameter and 4" in depth, should be collected from the affected area. The samples should be collected randomly throughout the area, then mixed together thoroughly and about a pint of this soil mixture transferred to a plastic bag for submission to the Clinic. Mail the sample as quickly as possible! If the sample cannot be mailed immediately, keep it refrigerated or out of direct sunlight.
After all this work, don't forget to provide the Clinic with site and plant information. Our sample submission form* illustrates the type of information we need. However, If you don't have one available be sure to include a detailed letter. Include a description of the problem (photographs are helpful) and indicate the plant species involved at the site. Describe the symptoms. For example, are the plants wilting, yellowing, and/or spotty? Is only one type of grass being affected? What is the soil type and how is the drainage? Are the symptoms distributed across a large area, in a high area, in a low area, or only in the shade? List any and all pesticides and fertilizers that have been applied to the site.
The Plant Disease Diagnostic Clinic is designed to provide you with diagnostic and educational services. Please feel free to contact the Clinic with any questions prior to your sample submission. The Clinic staff work hard to provide you with fast, accurate results. Providing answers to your important questions prior to sample submission may enable us to get you the answers you need on a more timely basis.
*Note: The sample submission form and submission guidelines can be found on the Clinic website (PlantClinic.cornell.edu), or contact Karen Sirois at the Plant Disease Diagnostic Clinic, Cornell University, 334 Plant Science Building, Ithaca, NY 14853.
John A. Farfaglia
Extension Educator