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    Pear rust

    The disease is caused by the fungus Gymnosporangium sabinae (or G. fuscum) and is common in Europe and other regions around the world. The disease is easy to be recognized by the bright orange-reddish spots appearing on pear leaves during the summer.

    The fungus has a complex biological cycle as it requires a metabolically active host continuously to survive. Alternative hosts apart from pear (Pyrus calleryana – decorative pear; Pyrus communis – common pear) can be decorative or forest trees of the genus Juniperus. The latter ones are conifers and evergreen and therefore can nourish the fungus during the winter.

    In the autumn, fungal spores (aeciospores) that are produced in special formations on the bottom surface of pear leaves disperse and infect young Juniper stems. Early Summer the reverse phenomenon is observed: Basidiospores, produced in special formations on Juniper stems infect neighboring pear trees.

    Symptoms

    Symptoms on pear trees appear in the spring as yellow-orange spots of 1-2mm in diameter on the upper leaf surface while young stems and fruit can also be infected. Leaf spots extend gradually and get a bright orange – reddish color. Small black dots (pycnidia) appear in the center of the spots by mid-summer. Towards the end of summer, brown bumps are formed on the lower leaf side just below the upper spots and conical protrusions develop (aecidia) in which aeciospores are produced. The aeciospores are released, dispersed by the wind and eventually infect young stems of Juniper trees.

    Importance and control

    Usually overall damage from the fungus is not so severe as to threaten the tree health. Of course, pear production can be significantly affected especially when infection of leaves and young fruits is extensive which can cause defoliation, reduction of photosynsyntic capacity, weakening of trees and yield reduction.

    Usually there is no need for special control measures. Sprays with protective or systemic fungicides (dithiocarbamates, triazoles and/or strobilurins) that are made for pear scab also keep pear rust at tolerable levels.

    Author/photos: Aris Chloridis

    Magnesium deficiency on tomato

    A typical case of magnesium deficiency in tomato plants, in a field in the region of Kavala, N. Greece. Interveinal chlorosis on old/mature leaves at the base of the plant is evident. Application of a foliar magnesium fertilizer was recommended to correct the condition quickly and avoid severe impact on the quality and quantity of production.

    Usually magnesium deficiency occurs in soils with a low content of magnesium and in light and acidic soils in which magnesium is easily leached. In soils with a pH from 4.5-5.0, any addition of magnesium to the soil leads to excessive and rapid leaching of the element. In these cases, use of dolomite is recommended for the simultaneous rise of pH and administration of magnesium. Application of magnesium sulfate or magnesium oxide to the soil can also correct the shortage of magnesium when pH is elevated.

    Shortage of magnesium can also occur in soils with high salinity and where large quantities of manure or fertilizers rich in potassium have been used. Finally, it can occur in soils with nutrient imbalance caused by excessive administration of potassium or calcium.

    Author/photos: Aris Chloridis

    Zinc deficiency on walnut

    A case of severe zinc deficiency on a walnut orchard in the area of Kavala in N. Greece. The deficiency already caused necrosis and fall of a large percentage of the foliage which is expected to induce quantitative and qualitative loss in walnut production.

    Usually zinc deficiency appears in acidic and zinc-poor soils, in light soils which are poor in organic matter, in calcareous soils which cause drop of zinc solubility in the soil solution and in cases where phosphorus fertilizers were used in excess.

    Author/photos: Aris Chloridis

    Cotton bollworm (or Corn earworm or African bollworm)

    It is the caterpillar of a moth, which is the fear of cotton farmers in Greece due to the extensive damages it causes to squares, flowers and bolls of cotton and due to its difficult control. The scientific name of the pest is Helicoverpa armigera (or Heliothis armigera) and is one of the most destructive insect pests of cotton, tomato, okra, pepper, tobacco, corn and others.

    The insect has 3-4 generations a year depending on the climatic conditions of the area and develops large populations from July to September, usually with a culmination in August when it causes the biggest damage to cotton. Fortunately, after a number of years with large populations and subsequent severe infestations, 2019 was a year of minor damage by cotton bollworm.

    One caterpillar is not limited to a cotton boll or fruit of another plant. It can infest many organs or many fruits within a few days by eating them superficially and then moving to others, thereby multiplying the quantitative and qualitative degradation of production. Caterpillars rarely cause leaf erosion. Usually infestations are on the reproductive organs (flowers and fruits).

    In general, the difficulty of insect control in cotton, especially in August, is due to the following factors:

    – Bollworm population structure in August (the most destructive generation in cotton) is mixed with all stages present: eggs, caterpillars, pupae and adults. It is therefore difficult for any insecticidal treatment to focus on the most sensitive stage of egg hatching and young caterpillar

    – In August, cotton plants are tall and cotton rows are closed so insecticide spray (with a horizontal bar) does not reach and cover the lower foliage of a cotton plantation

    – Insecticides used today act mainly through stomach and secondarily through contact, so caterpillars that feed and live on the lower layers of cotton foliage are not properly exposed to the insecticide

    Author/photos: Aris Chloridis

    Blossom End Rot (BER)

    A physiological disorder of a plant during the stage of fruit development and growth. It is a quite common problem on tomato, pepper, eggplant and zucchini which is caused by the (usually transitory) low calcium concentration in fruits. The disorder appears most commonly in cases where watering is irregular or in periods of drought and plant stress which induce the transitory decline in calcium absorption and movement in the plant.

    Calcium deficiency can also appear during fruit development due to excessive fertilization with nitrogen and high temperatures which favor fast development of plants, high salinity and root damage during soil cultivation.

    Most of the times BER appears on the first tomatoes of the season as plants under stress at fruit set of the first inflorescence. Usually the problem disappears later in the season, on tomatoes of subsequent inflorescences.

    How you can avoid BER

    – Select varieties tolerant to the disorder
    – Water plants adequately and regularly
    – Mulch plants so that water evaporation from soil in minimized
    – Keep soil pH between 6.5 and 6.8
    – Use fertilizers poor in nitrogen and rich in phosphorus
    – Add calcium to the soil at planting, but only if calcium deficiency is proven. Usually calcium level is adequate in soil but it cannot reach fruits for the reasons explained above
    – Spray foliarly with a calcium fertilizer

    Author/Photos: Aris Chloridis

    Olive peacock spot or olive scab

    A very common and serious disease of olive in Greece, which causes weakening of olive trees and production decline due to the loss of foliage and therefore inadequate nutrition of trees. In cases of intense infection it can even eliminate production. Cause of the disease is the fungus Spilocaea oleagina. Infection by the fungus is favored by wet weather and medium temperatures, therefore it is more intense from spring to start of summer and in autumn. The disease is controlled mainly with the use of copper compounds.

    Author/photos: Aris Chloridis

    Grapevine Downy Mildew

    From a visit to a new vineyard (variety Jack’s Salute) of a farmer/partner of Agrocure in Kavala, Greece. The vineyard had quite intensive infection by Plasmopara viticola one of the most important grapevine diseases across the globe. Instructions were given to the farmer for the control of the disease although the current hot and dry weather conditions (end of July) will limit the spread of the disease.

    Text/photos: Aris Chloridis

    Rose black spot disease

    The cause of this well known and widespread disease of the roses is the fungus Diplocarpon rosae (Marssonina rosae). It is the most common and serious disease of rose. The fungus infects the leaves in the spring as it is favored by the spring dew, rain and moisture on the leaf surface. By contrast the high temperatures of June, July and August stop the growth of the fungus. Small brown-black rounded spots appear on the top surface of the leaves which expand gradually.

    Affected leaves may turn yellow and fall eventually, a phenomenon which starts from the old leaves of the plant base. In some cases, the spots remain small and the leaves do not fall. Another symptom may be the appearance of small purple-black spots on tender shoots. Severely affected plants may lose most of their foliage and remain stunted and vulnerable to other adverse conditions.

    Common control measures:

    1. Remove and destroy infected leaves and shoots. Also, remove all infected fallen foliage
    2. Keep foliage dry therefore do not water with sprinkler
    3. Use of fungicides: chlorothalonil, copper fungicides, difenoconazole, mancozeb, penconazole, potassium phosphonate, prochloraz, sulphur, thiophanate methyl, ziram.

    Bitter Pit in an apple storing facility

    Bitter Pit on Granny Smith apples. Bitter Pit is a physiological disorder of apples which most of the times appears post-harvest, during apple storage in cool rooms. Calcium deficiency and calcium/potassium imbalance are the main causes of this condition.

    The problem can get worse in cases of excessive Nitrogen or Potassium fertilization or if Boron is in short supply. Also excessive pruning and thinning lead to big-sized fruits which are more prone to the Bitter Pit condition.