A variety of plant diseases and many types of pests can devastate a crop of sweat peas; unless certain measures are taken to protect the plants. Given below is a fairly comprehensive list of likely problems that can destroy a sweet pea crop. The list may look very alarming; however, most of these problems are rare and will not be encountered by the majority of gardeners.
Anthracnose is a fungal disease which is not known in many European countries like Britain which enjoy a cold climate all year through. However, this fungal disease can devastate sweet pea crops in the warmer areas of the world, such as the southern states of the United States of America. The signs of anthracnose infection immediately evident on sweet pea plants include brittle young shoots. Plants also have small white spots all along the shoots, the leaves and the flowers. These white spots are markedly evident on the young growth initially but have a tendency of spreading down the plant soon; the result of infection is wilting of the plant followed by the death of the plant. There is no known treatment for this particular fungal disease.
Aphids are a very common plant pest. These familiar sap sucking insects infect many plant species. In sweet peas, they can induce a weakening in the growth of the plant if left undisturbed. However, they can become dangerous for the plants as they often act as vectors that transmit viral diseases and can thus be considered one of the most significant problems causing pest as far as sweet peas are concerned. With respect to sweet peas, the common pea aphid, which is a relatively large creature for an insect and which has yellow, pale green and pink coloration, is one of the species of concern, however, some other aphid species can also bring great trouble to sweet pea plants.
These aphid species of concern can easily be controlled by the few legal systemic insecticides still on the market -these powerful insecticides can do a good job of destroying most pests. In addition, many of the less toxic contact poisons and milder insecticides can also be used for controlling these pests. However, for the latter type, thorough, well directed and careful spraying may be required as they are contact poisons as implied by the name. These pest poisons have to come into actual contact with the insect body to kill it. Finally, the use of insecticidal soaps and other non-toxic alternatives is also an alternative, many of these control measures can also prove to be very effective, here again, and successful destruction of the insects will depend on the amount of care taken and thoroughness of use.
Blindness in sweet pea is a physiological problem that can stunt plant growth. It is not a disease in itself. Afflicted plants which were previously healthy looking may begin to look slightly crumpled, then the shoots stop all growth - the condition is called blindness. Uprooting affected plants is the best remedy as there is no cure for the unknown physiological distress faced by the plant.
This mould induced disorder is most commonly seen in badly grown glasshouse cut flowers. Sweet peas grown in the garden are normally not affected by this disorder. However, unusually damp summers can bring on botrytis even in garden grown plants and the affliction brings on white flower spotting, this is especially marked in blue flower varieties. The appearance of brown spots on white-flowered varieties is another manifestation of the disorder in sweet pea plants. The infection also attacks as a grey mould elsewhere on the plant body and can kill plants. The home gardener is handicapped by the lack of effective chemicals in the market for the treatment of this disease. However, the home gardener is helped by the arrival of a hot, dry and sunny weather - which can immediately bring a big improvement in the situation as the infection cannot last in such weather.
Bud drop is a strange disorder in sweet pea plants. The problem causes the individual buds on the stem of the plant to fail to develop fully and these buds soon drop off before they have a chance to fully open up and bloom. This disease can be a disaster for the plant exhibitor, and can become a very infuriating experience for the gardener. The disorder seems to be brought about not by a disease inducing organism, but seems to be a physiological reaction of the plant to some external factors and the disorder often comes a week or two later then the appearance of sudden cold weather, perhaps combined with drying winds. Bud drop may also be induced by poor light condition; another factor could be excess of the mineral nitrogen in the soil in which the plants are being grown. One of the most obvious causes of this disorder is an extreme drought or lack of moisture in the soil. However, this problem at least can be solved by constantly keeping the roots in a moist state.
Sweet pea varieties differ in their ability to cope with the disorder. Certain sweet pea varieties seem to be much more prone to facing the bud drop disorder than other varieties but the actual effect on any given sweet pea variety can vary in different seasons and depends also on the soil type on which they are grown.
Crown gall is a bacterial infection of sweet pea plant. The bacterial infection usually begins when contaminated water is splashed from the soil on to small openings in the stem - caused by physical injuries to the plant. Crown gall begins as an area of irregular swelling at around ground level on the stem. There is no cure for this infection; however, the disorder is usually more alarming than it is harmful - leading to the death of the plants only in the rarest of rare cases.
Leaf scorch is perhaps the most commonly observed in sweet peas grown in cordons on light or sandy soil, however, it is unusual in sweet pea plants grown using other soil types. The effects on the plants is gradual, initially, the color fades from the lower leaves on the stem, however, the plants keeps growing fairly well and is not affected much at this stage. However, as time passes, the effect increases and plant growth inevitably slows down to such an extent that the plant becomes useless. This problem is said to be more common in the scarlet and orange sweet pea varieties. It can be avoided by light shading and adding organic matter to the soil from time to time.
Leafy gall is a sweet pea disorder induced by bacterial infection. It results in the formation of clusters of unnaturally short, thickened and distorted shoots, these growth are mostly developed on the lower parts of the plant. In sweet peas, this bacterial infection causing leafy gall might be contributing to incidences of blindness.
Sweet peas are rarely afflicted by this uncommon disease. The causative organism is usually found in the soil; the mode of infection of the flowers is still a mystery and needs to be investigated. The best practice is to avoid growing sweet peas again on the site where the problem was initially encountered. Seeds from infected plants must also be destroyed as the disease may also be transmitted by seed.
Leatherjackets are the larvae of the crane fly which can occasionally cause great damage to directly sown sweet pea seedlings in an open garden. In the old days, the problem was easy to handle because then direct sowing was far more common, and the sowing rate was very high to permit the leatherjackets to a few plants without them ruining the final display of flowers - however, directly sown sweet pea plants in a small garden can be completely damaged by this infestation. The problem is considered only troublesome where a lawn has been dug up or turves have been used in the trenches meant for growing sweet peas.
Mice are very devastating to seed pots of sweet peas. The mice cause problems by digging up and eating all seeds and may consume an entire stock in one night if not checked. An infestation of mice can be checked by putting seed pots in frames and ensuring that the lids fit tightly and than setting traps among the seed pots to snare the mice. Where the use of traditional mouse traps is preferred to the use of used live traps, the gardener must ensure to set each trap under a 12.5cm (5 inch) flower pot raised on stones or along the length of a drainpipe. This precaution must be taken to prevent the accidental snaring of birds and other small animals which are harmless.
The mice will continue to be a threat to the plants even after the sweet pea seeds have germinated, because the young shoots will now merely serve as markers for the seed below them - these can be quickly dug up and devoured by the mice. The traps must continue to be laid until this danger is past.
Mice become less of a danger once the sweet peas have been transplanted in the garden. Mature plants are not likely to be damaged by the mice anymore, although the mice will on occasional even nibble at shoots if food is rare. The most vulnerable stage for the sweet pea is when the seeds are sown direct on the soil. At this stage, they are particularly vulnerable, and again, traps should be set to capture the mice. Proper storage of seeds in a place where the mice do not have access will be a good precautionary measure.
Mildew (downy) is not similar to powdery mildew, though it is sometimes confused for it. Sweet peas affected by downy mildew is a relatively rare phenomenon and its likelihood of occurrence is increased by prolonged cool and damp conditions in a region. Affected plants will show some yellow patches that become visible on the upper surfaces of the leaves while the underside of the leaves shows patches that have a purple tint - as the disease progresses, a white mould appears on the plant body. The infected parts of the plant will in time turn brown and die off if left untreated.
Popular garden stores stock good fungicides that can be used to control this disease on individual plants, however, controlling the fungus over an entire crop is harder to achieve. Other popular garden plants such as peas and broad beans are also attacked by the same mildew, however, each of these host plants is more susceptible to its own unique race of mildew and therefore cross infection across different types of plants does not occur.
Sweet peas are most susceptible to this common fungus. Indeed this may be the most usual fungal disease that is observed in sweet peas. When plants are affected, the infected plants begin to show small and grayish white spots or patches appear on their leaves. Soon these spots start to coalesce and spread out to include the flowers. After some time, if the disorder is left untreated, the leaves may start to turn yellow and in severe cases will then wilt and fall off.
Weather plays an important part in the occurrence of powdery mildew. The disease is most evident on sweet peas when there is a long hot, dry spell of weather with very low humidity in an area. The impact of the disease on the flowers can be minimized by keeping the flowers on the plant well watered at all times under these weather conditions. Organic as well as inorganic fungicides are available in the market to counter the problem. If the dry spell persists, repeated application of fungicides may become necessary to maintain the sweet pea plants in a healthy state.
Sweet pea is not vulnerable to infection from the species of powdery mildew found on roses, however, the mildew species that attacks lupins and peas can also infect sweet peas and this is a factor to be carefully considered while planning the cropping of sweet peas with other plants in the garden.
Pea weevil is another pest of the sweet pea plant. This insect pest causes very distinctive damage to the sweet pea plants. This irritating pest forms a series of neat notches on leaves; these are formed when the adults eat out the edges of leaves. Though the pea weevil is most often seen in culinary peas - Pisum sativum spp. - and other plants, especially clover, sweet pea is also affected. The seedlings can be set back in spring once the adult insects emerge from winter hibernation and feed on foliage; these adults then produce young insects feeding on the root nodules later in spring and early summer. When the next generation produced by these young insects hatch late in summer, the sweet peas are not likely to be molested - as the insects will prefer younger, juicer material and move on to other plants. Pea weevil can be controlled by some insecticides that can kill the adults and prevent their breeding on the plants.
This insect can also affect sweet pea plants. These tiny black beetles are often found on sweet pea flowers, the keel of the flower being a preferred location for the insects. They are not very damaging to the plants and are more of an eyesore than a pest. The pollen beetle infestation can be controlled and the insects eradicated by placing yellow buckets half full of water near the rows of sweet peas. These beetles are attracted by the yellow coloring of the buckets and will come down and drown in the water in the buckets.
This fungal disease is also capable of destroying sweet pea plants. When speaking of the "foot" of the sweet pea, the reference is not to the root, but to the point or area at which the stem joins the root of the plant. The fungal infection that causes the rotting can move up to this point from the root where it started or move down from the foot downwards into the root system - in both cases, the plant will suffer. Sweet pea crops often suffer from a familiar disorder called the damping-off disease; this often affects weaker seedlings usually but not always. The damping-off disease can be considered to be one specific type of foot rot and in affected sweet peas the damage is most common when the plants are small. Affected plants will stop growing completely and will quickly wilt away; often black lesions can be seen on the remnants of the root system of dead plants.
While sweet pea seedlings are the most likely to be affected by the disease, on occasion, mature plants can also be affected and though it is tempting to suggest that this susceptibility of mature plants is due to some vague inadequacy in a particular seedling - it may not always be so, as even robust plants can be affected. Infected sweet pea plants show certain physical characteristics, the roots will often be found to have a black discoloration. The gardener must consider moving the sweet peas to another site in the garden to ensure that future crops escape the infection.
The disease is often brought on by the Pythium and Phytophthera fungi species, but other species including Thievaliopsis have also been implicated. These fungal organisms are normally present in garden soils most of the time and will attack plants when the plants have some weakness or are under stress from another cause - internal or external. This fungal disease can damage sweet pea plants grown in seed pots or those being grown in the open ground in the garden. This fungal disease is especially likely to attack plants when the soil or compost is extremely rich in nitrogen and so the excessive use of fertilizer or manure should be avoided to prevent the occurrence of this disease.
The presence of root nodules can prove to be extremely worrying to novice growers of sweet pea plants, especially when the plants are being grown outside or when they are being removed and cut in the fall. The clearly visible small lumps that are present all over the roots of the sweet peas plants tend to alarm the novice. An infection might be immediately suspected by the beginner. These root nodules are harmless, and root nodules are an integral part of plants in the pea family and contain bacteria which help the plants. The bacteria in the nodules help the plant fix atmospheric nitrogen by assimilate nitrogen from the air into the soil and thus making it available to the plant in an inorganic form. All leguminous plants have these nodules, and as sweet peas are legumes, these 'nitrogen fixing' nodules are an essential feature to them.
Sclerotinia is rare infection in sweet pea plants. The condition is also known as cottony rot in the USA, and is most prevalent in plants that are grown in damp areas. The disease attacks the sweet pea plants at the base of the stem, symptoms can be noticed at the leaf joint or between leaflets where a fluffy white mould becomes visible. The wilting of the plant and subsequent death often follows or is associated with the appearance of this mould. The best way to prevent an infection of the entire crop is to burn up affected plants. The gardener must carefully dig up all affected plants and burn the plants. The best solution is to move the sweet pea bed to another site in the garden for at least three years after the first infection was noticed.
Sweet pea seeds often rot in their pods before they can germinate and produce plants. This situation must not be confused with a failure to germinate due to the hard seed coat failing to admit sufficient moisture for growth. The rotting of seeds is usually brought about by the agency of one of the damping-off fungi, the Pythium species of fungi in particular, and the rotting and destruction of seeds can be exacerbated in sweet pea varieties with very soft seed coats or in poorly produced seeds by the same fungal agents. The result is that many sweet pea seedlings will simply fail to appear as a result of the rotting and destruction of seed material.
Some precautionary measures can be taken. It is important to avoid firming the seed compost down to hard when filling up the pots. It is also necessary to avoid over watering the soil in the seed pots and to never water them with water sourced from a rain barrel - as the water may be contaminated with fungal spores or bacteria.
The sweet pea plants can also suffer from infestation from slugs and snails in the garden. These animals are very familiar pests to most gardeners; they can become troublesome to sweet pea plant growers for two reasons. They can pose a danger in the seedling stage as well as being dangerous to mature plants.
These organisms may attack seedlings in the pots or in the open ground, and possibly nibble off shoots from the plants before these have an opportunity to develop and mature. Slugs and snails may also actually graze on the lower foliage of more mature plants, their attack can cause the leaves to look unsightly and reduce their vigor and developmental potential. Slugs and snails can be controlled through the use of organic or chemical controls. Various traps and biological controls are also very effective in dealing with these common pests.
Streak is also a disease that can afflict sweet pea plants. While the original term was used to refer to a rare disease which brought on the development of reddish or brownish streaks on stems and leaves of sweet pea plants. The term "streak" is now sometimes used as a loose description for the yellow or reddish streaks that can be seen on any part of the sweet pea plant - though these can be brought on by a range of different agents. Streak is also used to describe the viral infection and flower breaking in sweet pea plants.
Thrips are tiny insects that are pests on many plants. They are also known as thunder flies or thunder bugs in some places. These small and slender insects, which are just over a few millimeters in length, are important pests of many kinds of common garden plants. Thrips infestation can not only cause mottling and silvering of young foliage and shoot tips but they can also be responsible for the transmission of the tomato spotted wilt virus from one plant to another. Thrips can be controlled by chemical control methods which are not difficult to carry out. The chemical preventive spray must be used at the first sign of damage on the sweet pea plants.
As with many plants, viral diseases prove to be the most serious problems for enthusiastic sweet pea growers around the world. Viral diseases are hard to control and devastating to crops. Sweet peas are affected by at least eleven different viruses. However, the viruses that infect sweet peas and cause significant damage are only five in number; the colloquial names such as "streak" or "mosaic" or the more formal names like the pea enation mosaic virus disease.
Viral agents are transmitted to plants by infected aphids or thrips that have been feeding on already infected plants; these are more often than not, related plant species such as the clover or culinary peas. However, viruses that affect weeds and other unrelated hosts can also move from these plants to the sweet peas through the agency of thrips and aphids. The virus stays in the insect body and moves with the insect to the sweet peas where the virus is transferred as the insect feeds on the sap of the plant. A good preventive measure is immediately apparent, as keeping plants free of pests such as aphids and thrips can keep viral infections at bay. The control of pests must be carried out together with the control of weeds and it is also necessary to ensure that all other plants in the garden are free of pests - as most viruses can infect many different plant species. It is not possible to take corrective measures, once a plant has developed the disease and shows signs of the infection. The only remedy is for all infected plants to be pulled up and burned to avoid possible transmission of the virus in the future. While, these infective viral agents do not persist in the soil, there is some evidence that it can be carried in the seeds of sweet peas. Some of these viral agents can also be carried on secateurs; as they can also spread from one plant to another plant during the dead-heading process or the removal of side shoots.
Sweet peas are significantly affected by five viruses as given below:
White mould is relatively speaking, a rare disease that affects sweet peas. It is also at times called the ramularia leaf spot disorder. The white mould is at times confused with the powdery mildew disease, however, unlike the latter, this disease tends to affect sweet pea plants in cool and damp conditions rather than in hot and dry weather. The physical symptom of the disease varies greatly from one plant to another. The appearance of a white mildew like covering on the leaves and the stems of the plant are the first signs. The presence of water soaked spots without definite margins on the stems is also a good indication of infection. These symptoms of infection in the plant are usually found in the leaves on the lower parts of the plant, usually the lower leaves turn yellow. This yellowing normally starts at the base, then the leaves drop off and the infection cycle is completed.
This disease is encouraged and exacerbated by the overhead watering of plants as this can create a damp atmosphere which gives a chance to the disease to develop. This is particularly true in bush-grown plants, and the disease can also be spread by water splashing from the soil.
The white mold disease is specific to sweet peas and other plants do not seem to suffer from the same disease. Therefore, infected sweet pea plants cannot spread the disease to other plants in the garden. The main mode of transmission of this disease is by infection from older plants, from year to year. The old plants left standing pass it on to new plants, the plants on compost heaps and plant parts can also spread the disease to other plants as well. White mold is not a very easy disease to deal with. Though, spraying can be effective, most of the really effective chemicals have now been removed from the market and the very few chemicals that can still deal with the disease may soon also vanish from the shelves in the near future. The best option is to transfer the site once an infection is detected. Growing the sweet peas some where else for a year or two will preclude any chances of the disease from spreading. The gardener must also be scrupulous about destroying the old plants in the fall-burning.
Wilt is another sweet pea disease that is usually caused by fungal species such as the Verticillium or the Fusarium fungi. One of the main effects of the fungi is to block the xylem of the plant - these are the internal channels which take the plant sap up into the plant and transport fluids - the harmful result is the blockage of fluid movement inside the plant. The plant is harmed severely and as the name implies, it results in the wilting of the plant. The effect of the disease may not be dramatic on initial observation. To the gardener, the plant may even seem to recover overnight; however, this is only temporary and the plant only wilt again under the heat of the day. In some cases, and rather strangely at that, the effect on the plant may initially only be visible externally along one side of the plant. In other cases, the effect on the infected plant will become immediately evident and the plant will show the symptoms quite suddenly on a hot day at peak season - this is much like the sudden fall down of clematis attacked by its own wilt.
Wilt brings out physical symptoms in sweet peas that can be very similar to the symptoms induced by foot rot disease, however, when the infected plant is dug up and destroyed - by burning as it must be - one must check the plant for proof of wilt. To get this proof, the uprooted plant must be cut cleanly through the stem at a height of 60cm - 90cm (two to three feet) above ground level. The presence of a brown staining in the cut surface is evidence of wilt.