Pests and diseases
There are many pests that like and want to attack the tomato plant and its fruits, and many of these must be dealt with in time if the harvest is not to be seriously jeopardized. Nowadays, there are rarely any pesticides to help us, so it is important to check the plants carefully on a regular basis, preferably every week. Insect pests are often found on the underside of the leaves, and by using yellow stickers and examining the catches carefully, an infestation can be detected and countermeasures taken early.
Aphids often attack the young plants. Aphids multiply quickly and all infestations must be stopped in time before it becomes unmanageable, use plant care products, soap or similar. It is also usually possible to squeeze the insects between your fingertips or to wash the infested parts of the plant with cold water. Don't forget to repeat the treatment, as there are always some that manage to escape the treatment and quickly multiply again.
Whitefly is also an insect that often appears in cultivation. They thrive especially in confined, dry and warm spaces such as on a warm sunny windowsill or in a greenhouse. The insect has several stages, but it is the adult flying animals that do the most damage by sucking sap from the young parts of the plant. In severe infestations, the leaves can become heavily soiled by the insect's excrement, in which various fungi quickly grow and form a dirty black film. This film prevents light from reaching the leaf, causing the leaf to dry out and wither. Use plant care products or soap to control the infestation. Another very good way to control whitefly is to use the yellow sticky pads available on the market. These are completely non-toxic and the flying insects are attracted by the yellow color and once they are stuck in the glue, they cannot get out. The discs also work well against all other flying pests such as fungus gnats and thrips.
Root diseases can occur if you grow in the same soil for several years in a row, which is often the case when growing in beds in greenhouses. A collective name for this group of pests is often referred to as 'soil fatigue'. No pests are visible to the naked eye, but are microscopic organisms, often nematodes, that attack the roots of the plant. The best remedy is to change the location every year, but in a greenhouse this is often not possible. Instead, the soil is improved with a good mix of compost, well-baked manure, grass clippings and so on, or all the soil is replaced. The soil that is removed can be used for all other plants but not for tomatoes or peppers, which are both attacked.
Spiders, or spider mites as they are also called, are millimeter-sized arachnids that suck plant sap from the plant. At the same time, it spins a fine spider web close to the leaves, and in heavy infestations it looks as if the whole plant is wrapped in cobwebs. The animal can cause damage mainly during early plant growth, and less frequently during summer cultivation. Spiders thrive in warm, dry and confined environments such as a hot window where tomato plants are crowded while waiting to be planted out. Seedlings that have stayed in the plant due to crowding, too small a pot, uneven watering and fertilization are the first to be attacked. A heavy infestation can quickly spread to other plants and it is therefore important to regularly check for spider mites. Check the underside of the leaves and especially those leaves that may look a little yellow-green-red and mutilated. A magnifying glass may be needed as the spider mites are small. The main action is to ensure healthy and thriving plants that are not crowded. The right sowing time in relation to your conditions for planting out and a pot that is the right size in relation to the plant's need for water and fertilizer significantly reduces the risk of infestation. You can also use small beneficial insects that eat the pests, which is known as biological plant protection.
The vegetable moth is a beautiful moth belonging to the moth family. The adult insect does not cause any damage to tomatoes, but it is its voracious larvae that you need to look out for. Usually, the damage is not so extensive and the tomatoes are enough for both you and the butterfly. The infestation itself usually appears in late summer in August/September. The damage is noted by the presence of feeding damage on tomato fruits and leaves, but there is usually no trace of the culprit. If you look closely, however, you will find traces of the larva's excrement under the plant. The caterpillar, which is incredibly well camouflaged in green to more or less brown shades, has different colors depending on where it is located. If you shake the plant hard, the fat and thick larvae fall to the ground and can then be neutralized.
Fungal diseases
Fungal spores are all around us and also around tomato plants. However, this does not mean that tomatoes are always attacked by fungal diseases; on the contrary, they are very resistant to attack. When they are attacked by various fungi, it is often we growers who have failed to provide the plants with the right conditions, but on the contrary have done something wrong in the belief that the plants would benefit. When growing outdoors, fungi are rarely a problem, except perhaps when the summer and fall offer only rain, of course. When growing in greenhouses, the most common mistake we make is to have too little fresh air in the greenhouse caused by keeping it completely closed in the belief that it will be warmer and better for the plants. Instead, what we create is a hot, humid and stuffy incubator where the plants quickly fall victim to any fungi that might want to attack them. By always ensuring that moist air can be ventilated, preferably through a window in both sides so that there is little cross draught, the risk of infestation is significantly reduced. Good cultivation hygiene in the greenhouse is also important. Weeds, removed leaves and rotting fruit should always be removed from the greenhouse, not later but immediately. Otherwise, these easily become a breeding ground for fungal spores to spread further.
Powdery mildew appears on the leaves of the plant as a white, later gray coating. There are lots of different races of powdery mildew, but what they all have in common is that they are very host plant specific, i.e. tomato powdery mildew attacks tomatoes and not any other plant. The fungus can also appear as small semi-transparent spots to small rings on the skin of the fruits. These so-called ghost spots are only found on the surface of the fruit and never go into the depths of the fruit. Powdery mildew often appears at the end of the growing season and mostly only in greenhouses. Ventilating well often reduces the infestation but heavily infested leaves are often removed and put in the compost or buried.
Potato leaf mould is sometimes confused with powdery mildew but they are two different fungi. Both tomatoes and potatoes can be attacked, but most often the infection occurs via a previously infected potato plant. An effective way to avoid infestation is to keep the cultivation of tomatoes and potatoes well separated. When grown in greenhouses, infestations rarely occur; instead, the damage is usually seen on tomatoes grown outdoors. As a rule, the process is both rapid and brutal, with plants being completely destroyed in a very short time. The attack starts as brown areas that quickly spread on leaves and fruits and warm, humid, rainy and sultry weather are good conditions for an attack. Once an infestation has been identified, it is important to quickly remove both infested plant parts and seedlings. Throw these in the trash, not in the compost as they easily overwinter until next year.
Gray mold is common at the end of the growing season. The fungus, which is ubiquitous, can attack any part of the plant but wound areas on the stem, leaf stubs or cracked fruits are places that are often affected. It is rare for the fungus to cause damage in the open, but it is almost always crops in enclosed spaces such as greenhouses and hotbeds that are affected. It is important to maintain good hygiene standards in the greenhouse as the fungus attacks damaged or dying plant material first. Removed tomato thieves, weed trimmings or cut leaves on the ground combined with (overly) humid, stagnant air are gateways for the fungus. The best remedy is to ventilate the greenhouse and during the fall a window or door should always be left ajar to allow air circulation.
Velvet spot is a fungal disease that mainly affects the leaves of tomato plants. In late summer, scattered yellow-green spots appear on the upper side of the leaves. On the underside, a felt-like brownish-gray coating is found. The infestation usually starts on the older leaves of the plant but quickly spreads upwards in the plant. The growth of the fungus is favored and is dependent on high humidity and therefore it is usually only tomato plants in greenhouses that are affected. Measures include airing the greenhouse and ensuring good hygiene, i.e. removing older leaves to create air circulation around the plants. Once an infestation has been identified, it is important to quickly remove and destroy infected leaves and for the next growing season it is necessary to thoroughly clean the greenhouse as the fungal spores easily overwinter. There are resistant varieties and if you have had problems with velvet spot in the past, it may be a good idea to grow only such varieties!
Ghost spots, ghost spot - see powdery mildew
Physiogenic damage
Plants can be damaged or grow abnormally without being attacked by a fungus or insect pest and this damage is collectively known as physiogenic damage. The damage may be caused by one or more factors or by a combination of factors, and symptoms often appear some time after the damage has occurred. Plant growth may be stunted, often leading to secondary infestations of fungi, bacteria and insects, which can make it even more difficult to determine the primary cause of the damage. Common causes of physiogenic damage are sub-optimal levels of light, temperature and humidity.
Curled leaves
During early summer when growth conditions of light, heat and nutrition are at their peak, it leads to vigorous growth of the tomato plant. The plant can then sometimes appear with strongly curled leaves at the top of the plant. It is always only the young developing leaves that show symptoms, no others. This is no cause for immediate concern, but it may indicate that nutrient levels are a little high and it may therefore be time to reduce the nutrient supply slightly for a short while. Curled leaves do not usually affect the next harvest in any negative way. This damage should not be confused with aphid infestations or the presence of pyralids, read more about these two much more serious problems.
Green neck
The upper part of the tomato closest to the bracket does not color in, but is green to yellow-green in color even though the rest of the fruit has already turned red. This is because the fruit has been exposed to too much sun and heat on these parts, destroying the fruit's ability to form the red colorant lycopene. Lack of calcium can aggravate the damage. Measures include shading the greenhouse during the summer heat waves and fertilizing with a comprehensive fertilizer.
Cracked fruits
In late summer/fall, it is common for tomato fruits to crack at maturity. The reason is always that the growth inside the tomato fruit is stronger and faster than the skin has time to adapt to. The skin then becomes too small for the swelling fruit, resulting in cracking. There are several factors that influence the degree of damage. The most important factor is variety selection, some varieties are completely hopeless with the fruits always cracking in late summer. Unfortunately, it is very rare that the information is on the seed bag, but you simply have to try your hand.
It is also the case that if the fruits are left on the plant for too long after they are ready to be harvested, they crack easily. The countermeasure is to harvest directly when the fruits are ripe. Another factor that has a negative impact on the percentage of cracked fruit when growing in a greenhouse is humidity. Keeping a ventilation window or door slightly open at all times ensures that excessive humidity is ventilated out. You can also make sure that watering takes place in the morning so that it has time to dry up a little before the afternoon/evening.
Deficiency diseases
All plants need nutrition to a greater or lesser extent. Some substances are needed in large quantities, we call them macronutrients. Others are needed only in small amounts and we call them micronutrients. Deficiencies can occur for each of these substances and the symptoms of the growing plant can be more or less diffuse. By using good quality soil and regularly applying a comprehensive fertilizer, we minimize the risk of deficiency diseases occurring. Nutrients can be applied in different forms, organic and inorganic. In the home garden, organic nutrition is often preferable because it favors the soil's macro- and micro-organisms, thus strengthening the soil's ability to deliver what the plants want. Regular additions to the soil of compost, grass clippings and well-rotted manure are good ways to improve the soil in both the short and long term.
Pistil rot is the name given to the damage that occurs at the top of the tomato fruit. It is caused by a lack of calcium in the swelling fruit and severe damage can lead to complete fruit destruction. The deficiency can occur partly because the amount of calcium in the soil is too low, but it can also be because watering is too uneven. The damage can be counteracted by regularly fertilizing the plants with a comprehensive fertilizer and by watering before the plants go dormant. Some varieties are more susceptible than others and often large-fruited tomato varieties are more severely affected. Cherry tomatoes are generally less susceptible and rarely show symptoms.
Nitrogen deficiency
All plants need nitrogen (N) to a greater or lesser extent. Nitrogen is essential for the growth of new shoots, leaves and stems. Fast-growing plants such as tomatoes have a particularly high need for nitrogen, and a lack of it has a direct impact on the plant's health and growth rate. We also talk about mobile and non-motile nutrients in plants. The terminology indicates whether the plant has the ability to move a nutrient in the plant to another place where it is better needed at that time. Nitrogen is a mobile nutrient and the plant is therefore able to move nitrogen from older leaves, which then turn yellow, to younger leaves that are developing and have a high need for nitrogen during their development. A good early indicator is therefore that if the lower, older leaves of the tomato plant start to turn yellow, the nitrogen levels are too low. You can also look at the leaves of the whole plant, where the color should always be a lush dark green at optimal nitrogen levels. If the leaves are yellow-green instead, it indicates nitrogen deficiency. An immediate action is to supplement the plant with nitrogen using a nitrogen-rich fertilizer.
Magnesium deficiency
Magnesium (Mg) is a nutrient that all plants need. When magnesium is deficient, the leaves, especially the older yellow-orange ones, become light, sometimes brown, between the leaf veins. The deficiency makes the whole leaf look marbled and severe deficiency causes the whole leaf to dry out, wilt prematurely and fall off. By regularly fertilizing the tomato plants with an all-purpose fertilizer, the risk of damage is significantly reduced.
Other issues
Root diseases can occur if you grow in the same soil for several years in a row, which is often the case when growing in beds in greenhouses. A collective name for this group of pests is often referred to as 'soil fatigue'. Fungi and other pests are not visible to the naked eye, but are microscopic organisms that attack the roots of the plant. The best remedy is to change the location every year, but in a greenhouse this is often not possible. Instead, the soil is improved with a good mix of compost, well-baked manure, grass clippings and so on, or all the soil is replaced. The soil that is removed can be used for all other plants but not for tomatoes or peppers, which are both attacked.
Weedkillers, or herbicides as they are more commonly known, can sometimes end up in the wrong place and do a lot of damage. The tomato plant is very sensitive to these preparations and they should of course be kept far away from the plants for many reasons. In recent years, there has been a lot of talk about a substance found in some agricultural herbicides, pyralids, which have caused severe damage to garden plants including tomatoes and peppers. The substance is very toxic to some plants and affected plants show severe damage such as tightly curled tops that look generally diseased. In the tomato plant, it is the growth point at the top of the plant that is damaged and in severe infestations the whole plant dies in a more or less prolonged process. Once the plant is affected, there is no cure. Pyralids are currently one of the biggest challenges for horticulture with many documented damages. Entry points to the garden are always purchased products such as soil and fertilizer and then almost always in organic ones. The only way to avoid getting the toxin into your crop is to either produce your own soil and fertilizer or to completely avoid products that may contain pyralids until further notice.