Plant Nutrition

Over-fertilization and Soluble Salts Injury on Mums

Providing adequate fertility is important in maintaining optimum plant growth in mums. However over-fertilization can result in high concentrations of soluble salts that can cause injury to the plants seen in this photo. Chrysanthemums are among a number of plant species known to have susceptibility to soluble salts injury. Over-fertilization results in high concentrations of soluble salts in the medium. As the salts are translocated throughout the plant they accumulate at the leaf tip and margins and when they reach toxic levels they cause “salt burn”.

Edge Burn on Ornamental Cabbage

The hot, humid summer weather may have caused poor transpiration resulting to calcium deficiency in the ornamental cabbage. Leaf edge burn (tip burn) is a symptom of calcium deficiency.   Calcium is immobile in the plant therefore deficiency symptoms show up first on young growing leaves. In cabbage the young leaves are internal leaves. Margins of the inner leaves may turn brown to black.

Calcium deficiency - Ornamental cabbage

Hot, humid summer weather may cause poor transpiration resulting to calcium deficiency in the ornamental cabbage. Leaf edge burn (tip burn) is a symptom of calcium deficiency.   Calcium is immobile in the plant therefore deficiency symptoms show up first on young growing leaves. In cabbage the young leaves are internal leaves. Margins of the inner leaves may turn brown to black.

Heat, Disease and Garden Mums

Growing media temperatures soar in plants on black landscape cloth during heat waves like the one we are experiencing. Garden mums may exhibit signs of wilting during extended periods of 90 plus degree temperatures. Monitor root health and test growing media of garden mums now. Take random samples of plants out of their pots and examine roots carefully. The roots tell a lot about overall  plants health, often before the top growth shows symptoms. Signs of poor root health are blackened or rotted roots or the lack of roots, especially young feeder roots.

April Pest Message

Impatiens Necrotic Spot Virus (INSV) was diagnosed on Lobelia 'Hot Arctic Blue'.  INSV is spread from plant to plant exclusively by western flower thrips. The virus can arrive in incoming plant material and virus infected thrips. Symptoms include distorted leaves and brown spots that look like a thumb print.  Thrips cannot transmit the virus unless they acquire it as first instar larvae. First instar larvae must feed on virus-infected plants to acquire the virus.

Iron deficiency

Iron deficiency has been observed on petunias and calibrachoa. Symptoms appear as interveinal chlorosis, normally starting at the shoot tips, but often they occur throughout the entire plant. Sometimes the leaves of some Fe deficient plants turn almost white. Preventing Fe deficiency can be accomplished by controlling pH and using an iron chelate fertilizer. In addition to pH, cold media (cold roots) or poor root development will affect uptake of iron. Often, if growers put a few flats on the benches compared to the floor, early in the season, they will see a difference.

Over fertilization

Soluble Salts

A common problem often diagnosed this time of year with spring crops is excess soluble salts. Generally, this is a result of too much fertilizer in relation to the plants needs. Inadequate watering or leaching, or poor drainage can also result in high soluble salts.

Sometimes high soluble salts levels occur when root function is impaired by disease or physical damage. Always check the condition of the root system when trying to diagnosis a problem.

Low pH Problems on Geraniums and Marigolds

Edge burn is beginning to appear on geraniums and marigolds where growth medium pH is low (below 6.0). As pH decreases, iron and manganese become more soluble. Some plants are very efficient at taking up iron (Fe)/ manganese (Mn) in the tissue causing toxicity symptoms. See photos, "Iron Toxicity" Crops such as zonal and seed geraniums, marigolds, lisianthus and all types of impatiens are susceptible. This disorder is sometimes called "bronze speckle" due to the appearance of numerous small brown spots on the leaves.

Controlled Release Fertilizers (CRF)

High soluble salts and injured roots have been occurring as a result of improper use of controlled release fertilizers. Controlled release fertilizers, when used properly work well, especially in mixed planters and hanging baskets and for heavy feeders such as petunias. Some growers successfully use a half rate of controlled release fertilizer to supplement their liquid feed program for these crops. However, using too much (not measuring accurately), or not distributing it properly when using it as a top dress can cause problems. Examples of common problems:

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