Leaf spot disease is a problem faced by many commercial growers owing to the pernicious nature of the fungi and bacteria that are responsible for them - combining rapid growth and easy transmission can lead to poorly salable, unhealthy crops if left unchecked and untreated. Copper oxychloride Demildex from African Pegmatite is a highly effective solution, rapidly preventing the reproduction and spread of the organisms responsible.
Leaf spot is a very common plant disease that even the most conscientious gardener is expected to see at least once in their vegetation. They are caused by a wide range of fungal species, as well as, some bacteria. Regardless of what the causative agent is, the prevention and treatment involve about the same practices.
Bacterial Leaf Spot: Tomatoes and Celery
The symptoms of plants affected by bacterial leafspots are numerous, with variable coloration the most common and first noticeable symptom. Infected plants are usually seen with black or brown water-soaked spots on their foliage or in some, a yellow halo which is usually uniform in size. Generally, the spots increase in size and grow into each other in the rainy season or under wet conditions as the case may be. In dry conditions however, the spots appear speckled.
As the spots grow in number, the entire leaf might become yellow, wither and drop from its branch. The most susceptible plants to bacterial leaf spot are members of the Prunus family which include almond, cherry, plum, apricot and peach. The fruit of these trees would usually have spots or sunken brown portions. These aren’t the only crops vulnerable to bacterial leaf spot. Vegetable plants like tomato and pepper crops are also at risk.
Causes
For celery, the bacteria responsible for leaf spot is Pseudomonas syringae, with early symptoms being small yellow spots on early leaves. These will enlarge with time and a rusty coloured circle may form around them. Bacterial spot disease in tomatoes is caused by four species of the genus Xanthomonas.
Transmission
Transmission of both types of bacteria responsible for spot disease is by water - typically most pronounced in times of high humidity and or warmth. Therefore, growth in greenhouses may be more conducive to bacterial transmission, owing to repeated heating and cooling cycles with a moderate humidity level maintained. As with many biological pathogens, those arriving on an already weakened plant will have the most impact. Most concerning for members of genus Xanthomonas is that the bacteria is known for rapid spread, with the pathogen able to transmit to non symptomatic plants over the course of a week from symptomatic plants several metres away.
Fungal Leaf Spot: Strawberries and Passion Fruit
Fungal leaf spots on the other hand attack lettuce and some other vegetable crops like (broccoli, cauliflower, tomatoes, peppers and turnips). They are caused by pathogenic fungi. Once the fungi gets into the leaves of the plant, they continue to grow until the leaf tissue is destroyed. Its resulting spots varies in size, from as small as a pinhead spot to one that covers the entire leaf. The dead sections on the leaves of the plants are usually of the colors, tan or reddish, brown or black. In some rare cases, the border of the leaves could turn red or purple. They are generally found in flowering plants and even indoor potted plants.
Leaf spots are most active under moist conditions and warm temperatures, for example, during the summer months. During this period, especially if the plants are being watered by an overhead sprinkling system, there’s just enough moisture to promote infection when the bacteria is either splashed by water or blown on to leaves by wind. Rain and wind are the main culprits for the transmission of the bacteria from plants to plants.
Fungal leaf spot disease is rarely severe enough to cause complete crop failure. However, modest breakouts may cause premature falling of the fruits and excess spots and blemishes to the fruit and leaves can render some of the year’s crop unsellable.
Causes
The fungus responsible for leaf spot in passion fruit is Alternaria passiflorae, whereas for strawberries it is caused by Mycosphaerella fragariae. Symptoms on both plant types are similar - spots on the surface of the leaves and larger spots, sometimes even lesions, on stems and stalks. Blemishes and spots to the fruit are not uncommon - it is these which indicate that the disease has taken hold in the plant and prevention strategies are now useless.
Transmission
Transmission of the two fungi occurs in very similar methods. Both fungi overwinter as mycelium in fallen leaves and are spread to plants in the spring when the weather becomes warmer, with suitable amounts of rain and wind. Disease development for M. fragariae favours cooler daytimes with wetter overnight conditions. Development for A. passiflorae on the other hand is much more pronounced in warm and humid weather, especially where there is a leafy canopy present. Like many other fungal type plant diseases, these capitalise on already weakened plants and those that are at the early stages of their growing seasons.
Effects of Leaf Spot
The Leaf spot disease can have a huge effect on the productivity of plants and their overall well-being. To start with, leaf spot can cause lesions in trees and vegetable plants which in turn causes heavy defoliation as the disease further develops.
It also leads to lower productivity in plants as defoliation of leaves might interrupt the photosynthetic processes of the infected plant.
Leaf spot is generally not harmful to older plants, in younger plants however, the disease can spread really quickly and can make the plants wilt and in more infected plants can die.
Prevention and Control
There are a number of preventive measures that growers can apply to prevent the spread of leaf spot in your tomatoes, strawberries, celery and passion fruit gardens. The following are some of them:
Planting resistant varieties: Planting resistant varieties is a very effective way of preventing leaf spot in the aforementioned fruits and vegetables. It is important that you plant resistant varieties of each crop where possible as this will limit, if not completely thwart the development of leaf spot diseases in them.
Husbandry: Pruning your plants or staking them to improve air circulation can go a long way to prevent leaf spot disease, both bacterial and fungal. Improving air circulation starves the causal organism of moisture which it needs for its growth and transmission. While it is important to prune the plants, it is equally as important that only disinfected pruning equipment is used after each cut.
Gardening: Pruning your plants or staking it to improve air circulation can go a long way to prevent leaf spot disease. Improving air circulation starves the causal organism of moisture which it needs for its growth. While it is important to prune the plants, it is equally as important that you use only disinfected pruning equipment after each cut.
Mulching: Having cleaned the plant’s environment, it is now time to use a thick layer of mulch to cover the soil. Mulching the soil will not only tame the aggressive growth of weeds but prevent the disease pathogen from splashing back up onto the leaves of the plant.
Disease-free seeds: Since leaf spot in vegetables is partly spread by the planting of infected seeds or diseased transplants, care must be taken to ensure that these seeds are from a leaf spot free-stock
Isolation: You should isolate infected plants from others before treatment to prevent the spread of the disease.
Other preventive measures include:
- Keeping plants dry. It is recommended that you wet your fruit and vegetable crops in the morning so as to give ample time for the sun to dry the plants before night fall.
- It is also important that you do not overwater your plants. If you do, you might be encouraging the spread of the disease as its causal organisms thrive best under moist conditions.
- You should also keep your plants healthy so they are in the right shape to fight fungal invasion and indeed, any other disease. Early intervention and treatment of plants that appear dry or wilting could help them survive leaf spot if infected by it.
- For indoor plants, care must be taken to water the roots rather than the leaves. You should avoid watering the leaves especially if your potted plant are kept in a warm and humid room.
- You should keep your plant’s surrounding free from dead leaves and twigs. This is especially true of they have previously been infected by leaf spot from the plant.
In general, sanitation and water management are arguably the most important preventive measures for containing leaf spot disease. For water management, watering in the morning is best practice. You should also increase air spacing between plants by increasing the spacing between them, and perhaps, most importantly is making sure bigger plants are not shading smaller plants or blocking them from getting enough air.
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