Crassweller debunks horticultural myths at event

AFP Correspondent

BEDFORD, Pa. (April 11, 2017) — “Some products make outrageous claims,” Dr. Robert Crassweller said at the winter Appalachian Fruit Growers meeting. He sorted out information on a range of products for his audience of tree fruit growers.
He began with the advantages of foliar fertilization. Response can be rapid, plus it may not get tied up in the soil biome.  The cost is relatively low for some products. Also, growers only need small amounts.
The disadvantages of foliar fertilizers include the limited amount of nutrients that can be applied. The cost of multiple applications can be high, and there is a possibility of foliar burn. Some materials may not be soluble and may not be compatible with other agrochemicals.
Crassweller pointed out that roots take up nutrients by mass flow, diffusion and interception. With foliar feeding, one must look at the components of the leaf structure, and factors such as relative humidity, the drying time and the attributes of the particular product.
With respect to foliar feeding of peaches, he noted that most studies examined the effects solely on fruit quality; few studies have looked at leaf levels.
Foliar nutrient applications must gain entry to the leaf—they must penetrate the cuticle and epidermal cell. But once inside, the absorption is similar to absorption by roots. Crassweller emphasized that the cuticle offers the greatest resistance to absorption.
He pointed out that some foliar applications can be effective. Late season timing may be more effective due to weathering of the cuticle. However, he urged growers to do a cost/benefit analysis first.
Turning to whether calcium products for apples differ, Crassweller noted a a 4-year study in Massachusetts which compared calcium chloride, calcium phosphate and calcium chelate as foliar sprays for McIntosh apples. The final recommendation was 75 pounds per acre of calcium chloride.
Of eight calcium compounds tested, only calcium chloride and calcium lactate effectively reduced bitter pit. Calcium chelate did not increase tissue calcium, but did cause fruit injury. Crassweller said the decision to use calcium chloride or Stopit should be based on economics due to the higher cost of Stopit.
Alternate row middles, which were meant to control mobile insects, may not be effective. Thick, dense canopies may not allow spray to reach the fruit. Calcium is absorbed by the fruit, but is not translocated from the leaves.
Calcium spray success depends on the percent of calcium in the product, the number of sprays, fruit development, cultivar, plus air temperature and humidity during and immediately after application.
Crassweller stressed getting the spray to the fruit. He also pointed out that the total amount of elemental calcium determines calcium disorder control. The price of calcium should also be considered.
Another question relates to whether potassium affects fruit color. A Brazil report indicated ground application positively influenced fruit color, firmness and percent solids. In Italy, fertigating with potassium reportedly enhanced fruit color.
However, Crassweller noted that unless potassium is deficient there is very little response. In addition, as with other nutrients, there must be a concentration differential across the cuticle. Also, he said, “Be mindful of increasing the potassium/calcium ratio.”
Better ways to improve color, he continued, include cultivar and site selection, canopy and nitrogen management. For Honeycrisp, the crop load plays a part. Other strategies to try can be reflective mulches, evaporative cooling, and for chemicals, ethephon.
Crassweller then addressed whether soil biome enhancing products increase orchard production. Several products employ seaweed based technology and extracts, and some feature humic and fulvic acid materials.
These products are reported to aid root development, plant health and increase yields.
The symbiotic association with fungal microorganisms mycorrhizae help absorb phosphorus, zinc and copper.
The beneficial practices that influence mycorrhizal fungi listed by Crassweller include perennial crops, rotation with host crops, over-wintering cover crops, reduced tillage and low fertility inputs.
On the other hand, detrimental practices include high fertility inputs (especially phosphorus), fungicides and herbicides, frequent inversion tillage, long bare fallow periods and non-host crops such as brassicas and buckwheat.
In assessing whether the materials work, Crassweller said, “Maybe.” But he added, “Plants with a healthy environment free from stress will certainly perform better.” He included factors such as sufficient moisture and healthy, fertile soil.
In questioning whether the latter could be done without extraneous products, considerations could be the consistency of the product, whether the soil biome may be site specific, and that plants could shape microbial communities with their species-specific root exudates.
Measuring the scope of soil additives would also need to be evaluated.
Dr. Matthew Kleinhenz at Ohio State has posts on a website on crop microbial biostimulants at  areas/vegbiostimsferts. This site contains a database and reports ongoing research.