How Powdery Mildew affect Peppers and how to

How Powdery Mildew affect

Peppers and how to Prevent Stress on Plants

with temperatures soaring during the high intensity of abnormal rainfall patterns and subsequent high humidity, Powdery Mildew can take its toll – if not early detected.

In the production of sweet peppers Healthy Powdery Mildew is the most common peppers, with healthy-disease and it is of vast economical looking foliage importance. The only effective way around them. to control Powdery Mildew is to have a holistic approach on the production of sweet peppers. Example of Powdery Powdery Mildew in peppers grows Mildew on a leaf. within the leaf and can be latent in the plant for 21 days before it becomes evident as having already infected the crop. It can result in defoliation of the plants, from which recovery is production exceptionally slow. Hence, it is essential of papillae. During to monitor a crop carefully and react winter, there quickly. are less uptake During its infection of the plant, problems with Powdery Mildew utilizes nutrients magnesium and from within the plant, interferes with calcium; thereby photosynthetic processes, increases also a reduced transpiration, impairs growth and Powdery Mildew increases leaf drop and flower loss. problem can Generally, a 10% infection/infestation be expected will result in a 10% yield loss. at this time. Conditions that encourage the growth of Powdery Mildew include 15.5 to 27°C, although powdery mildew can survive at temperatures as low as 4O°C, low light intensity and Powdery Mildew has the ability to even germinate in the absence of water. On the other hand, suppressive conditions include water on the plant surface for extended periods of time, day temperatures above 32°C and night temperatures above 18°C, direct sunlight or high pH conditions on the leaf surface. The reaction of nutrient and environmental conditions is also important as under low light conditions, magnesium concentrations in the plant are reduced. Under conditions of high disease pressure, this low level of magnesium could make the plants more vulnerable as they are unable to build the papillae. Also, under low light conditions, there is also a reduced production of sugars by the plant which will also affect the during its infection of the plant, powdery Mildew utilizes nutrients from within the plant, interferes with photosynthetic processes, increases transpiration, impairs growth and increases leaf drop and flower loss. Understandably, the management of the irrigation and fertigation system is essential in controlling the infection. Pulsing has been found to be a highly effective irrigation technique that results in creating a low water tension in the soil medium and consequently increasing yields. Frequency of application is more important than the amount of fertilizer being applied, and this can be directly related to the increased availability of phosphorous and manganese. The importance of light in pepper production is little considered, particularly with regards to field pepper production. Plant density and the trellising of sweet peppers are all about sufficient light. A lack of light will not

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how PowDERY milDEw AFFEcT PEPPERs 10

only lead to poor yields but in the end it will lead to a high incidence of Powdery Mildew that may destroy the crop. Plant population and the direction of the rows should all be based on exposing the plants to as much light as possible. Fields obtaining large amounts of afternoon sunshine are less susceptible. Traditionally, planting was recommended to be done in a North-South direction, but it has been found that this can lead to early infections of Powdery Mildew, especially when related to light conditions. An East–West row configuration in winter may reduce the incidence of infection. In winter, it would be wise to reduce the plant density so as to increase the amount of light received by the plants. Summer population: 35000/ha, winter population 25–30 000/ ha. This would also help reduce the incidence of Powdery Mildew in the crop. A minimum light level of 1000psu (photosynthetic sun units) is required at midday for prevention of Powdery Mildew.

Further tips to avoid Powdery Mildew:

• Growing under protection under winter conditions (short days, low light intensity) one should use the

Dutch method of trellising to ensure maximum light penetration. • Air movement in the tunnel or in the field is also important and planting in the direction of the prevailing wind for field production will also be advantageous in reducing disease incidence. For tunnel production, maintaining a relative humidity of between 65 and 75% with air movement at 0.5m/s will also assist reducing infection • Soil preparation for peppers, as with any crop, is essential in good crop production. It also assists in the control of Powdery Mildew infections. A soil analysis is essential in ensuring that the balance of the nutrients in the soil is correct as this will increase the resistance of the crop. If the sum of the K and Na is greater than 10, there is reduced manganese availability and this will result in increased Powdery Mildew infection. If the calcium balance indicates excessive levels of calcium, an expected reduction of magnesium uptake can occur resulting in a more susceptible plant. • The amount of available carbon in the soil is also essential for adequate production. 6% available carbon assists in the production of active roots which helps with the development of strong healthy plants with a strong resistance to infection. The carbon content can be used to determine the amount of organic matter or compost that should be applied to the soil prior to planting. The use of organic matter and compost helps aerate the soil.

Poor air circulation in the soil can also result in the development of Powdery

Mildew infections. • The control of soil pathogens is also an important part of this process, particularly with regards to nematodes. It is essential to apply 3 applications of nematicides to catch all the phases of the growth of the nematodes. The nematodes reduce the manganese availability that consequently reduces the resistance of the crop to the disease. The use of indicator plants in the field will also assist in the identification of the presence of nematodes. Open field melons will show nematodes within 5 days. Also remember to test your water for the presence of nematodes. • Planting your seedlings correctly is also important. Seedlings should be planted only as deep as the top of the plug. Planting too deep causes the plants to be more susceptible to disease. This is because the plant is stimulated into producing lateral roots. This causes damage to the stem that in turn allows for an infection to occur. Also, these lateral roots may be less efficient at taking up nutrients as the crop matures.

Transplanting of younger seedlings is better as it allows for better root development. The ideal seedling should have 2 cotyledon leaves and 2 true leaves. Direct seeding should also be considered as it eliminates transplant shock. In Europe, grafting of seedlings is also a popular practice in helping prevent damage from nematodes.

Excessive applications of nitrogen have been found to excite Powdery Mildew. See attached guidelines on fertilization of peppers. It is better to apply fertilizer according to growth phases than to fertilizer requirement or by week as the length of the crop differs from season to season. • Oxygen in the root zone is extremely important, it assists in energy production, produces a healthy root system (longevity, health and yield), assisted by the incorporation of organic matter at planting, minimal compaction of the soil and prevention of over irrigation. Weeding however has been found to damage the feeder roots just below the surface of the soil, preventing nutrient uptake. • An integral part of your Powdery Mildew preventative program is fungal sprays and spray management. How effective is your spray? The ideal spray should Soil preparation for peppers, have a droplet size as with any crop, is essential of approximately in good crop production. it 400 um or 2984 also assists in the control of powdery Mildew infections. droplets/ml. For systemic sprays, 20 – 30 drops/ a soil analysis is essential cm2, whilst contact in ensuring that the balance sprays should be of the nutrients in the soil is applied at 50 – correct as this will increase the resistance of the crop. 70 drops/cm2 . Preventative sprays are really important, start early. Use only registered products. Bicarbonates of sodium or potassium have been found to be as effective as neem oil and sulphur burners. Systemic sprays should be followed by contact sprays. • Disease resistance, especially against virus diseases, is essential in the production of sweet peppers. The most important virus threats come from Tobacco Mosaic Virus (TMV) and Potato Virus Y strain 0 and strain 1 (PVY-0 & PVY-1). The latest development on this front is the resistance to Bacterial Spot (Xv), Tomato Spotted Wilt Virus (TSWV) and Root-knot nematodes (Ma). Finally, one should remember that disease resistance is lost as soon as plants experience stress. It is therefore ever important to ensure your greenhouse attendants are observant and diligent in reporting any plant stress • Again, the management of irrigation immediately. Delay in taking action is and fertilizer applications are essential directly related to loss in revenue. for the control of Powdery Mildew. JS