Methods of protecting carnations from Fusarium wilt and stem rots

This disease is invariably present in all carnation plantings and can cause immense damage. The pathogen penetrates the stems through damaged surfaces, such as growth cracks, or at the sites of lateral shoot removal. Flower cutting sites are potential entry points for infection.

Affected areas gradually girdle the stem, leading to wilting. The leaves on the affected stems change color from grey-green to straw-colored, and they do so very quickly. In a humid environment, the pathogen actively produces spores on the affected tissues; spores are easily spread by water splashes.

Carnation cultivars differ in their susceptibility to the disease. Plants prone to stem cracking at the base are more severely affected. As a rule, the damage is most severe in autumn, winter, and spring, i.e., at high relative humidity.

Control: The most effective way to combat Fusarium rot is to prevent an increase in relative humidity in the crop, especially in winter and at the beginning of emergence. When high-volume spraying with captan or benomyl is performed, disease development is halted. This is especially important in poorly heated greenhouses, where it is advisable to carry out spraying throughout the winter.

The symptoms of Botrytis and Fusarium stem rot are very similar. easily infects poorly growing plants, in particular through wounds or damaged tissues. The infected plant wilts, taking on a straw-like color. On the affected areas, a typical grey mold growth appears, especially in conditions of high humidity. In addition, small black sclerotia of the fungus are formed.

Spores are spread by air, adhering to various objects after touching the affected plant. The disease poses a danger to the crop only during prolonged periods of excessive moisture. Such conditions are usually created by insufficient heating, which is carried out to reduce relative humidity.

Control: An effective way to control the disease is to maintain the air relative humidity at a low level. If this is not possible, the following measures are applied:

• High-volume spraying with iprodione;
• Spraying with captan;
• Spraying with thiram.

Many populations are resistant to benzimidazoles (see page 131).

Alternaria shoot rot, alternariosis. This fungus causes not only root rot but also affects stems, penetrating them through damaged surfaces or growth cracks. As a result, black spots appear. For both types of damage, control methods are similar (see page 279).

Rust is a common disease of carnations. Brown rusty fungal pustules appear on the stems, leaves, and even on the calyx of the flower if the damage is epiphytotic. Often in the same planting, almost healthy plants grow next to severely affected ones. The infection spreads by air and water droplets, especially heavily in the autumn and winter months. Rust is often brought into the greenhouse with cuttings, which look healthy at the time of planting, since the incubation period (from infection to the appearance of symptoms) can last for three to four weeks. The presence of water droplets or very high humidity favors spore germination and infection development. At high temperatures (21 °C), rust does not develop.

т Fig. 12.2. Concentric circles of pustules on carnation leaves. m 7 M affected by rust (pathogen Uromyces dianthi!). % E Cancer. Control. All cuttings with ‹ з в =. signs of damage must be discarded. To avoid excessive surface wetting and high relative humidity, environmental parameters are monitored. For the development of a rust epiphytotic, ideal conditions are created by leaking roofs and gutters. In the fight against rust, spraying with benodanil, bitertanol, and zineb, as well as irrigation with oxycarboxin when growing carnations in peat bags, are also effective. Alternaria D м — ^ «5 { leaf spot or rot, alternariosis PI ль M —(pathogen Alternaria dianthi!) This disease is rarely a problem for flowering carnations. Small purple spots appear on the affected leaves. Under conditions of high humidity, they grow to 1 cm in diameter, with the edges remaining purple and the middle of the spots acquiring a grey-brown color. Black fungal spores form on the spots, giving the affected area a sooty appearance. Some spots become sunken, resulting in the death of the leaf. The spread of the fungus occurs mainly through water splashes.

Control. By maintaining low relative humidity in the greenhouse, infection can be avoided. If spraying is necessary, thiram or iprodione should be used, as they help suppress the disease.

The symptoms of this uncommon disease resemble those of Alternaria spot, except that the purple border of the lesions is less pronounced, and the center of the spots does not develop a black sooty coating, although small black pycnidia sometimes form. In general, symptoms of Septoria develop on aging leaves. Fungal spores are easily spread by water splashes. The main source of infection is infected cuttings.

Control. Infected cuttings must be culled, and the planting should be sprayed with zineb upon the appearance of disease symptoms. Leaf rot (Heteropatella valtellinensis)

Under conditions very unfavorable for plant growth (high humidity, low temperatures), this fungus attacks the bases of lower leaves, causing the appearance of black watery spots. As humidity increases, the spots turn grey and dry out. This disease is usually controlled by modifying environmental factors.

Ring spot, or fairy rings (Cladosporium echinulatum, syn. Didymellina dianthi, Mycosphaerella dianthi, Heterosporium echinulatum)

Reddish-brown spots covered with a black powdery coating of spores appear on leaves and stems. The spores are often arranged in concentric circles, which gives the disease its name. As with most other pathogens of leaf

285, spots, conditions of high humidity are favorable for this pathogen. Methods for controlling ring spot include reducing relative air humidity and spraying (high-volume) with benomyl, mixtures of benzimidazoles and dithiocarbamates, daconil, or dichlofluanid.

This disease is widespread but of little economic importance. The first symptoms, appearing on lower leaves, are a spiderweb-like pattern on the leaf surface, forming as the fungus penetrates under the waxy cuticle layer. When the entire leaf is affected, the waxy layer disappears completely, giving the impression that the leaf has been washed with a soap solution or detergent. The fungus develops only under conditions of very high humidity at the leaf surface.

Control. Fungicide spraying is usually unnecessary in controlling this disease. It does not affect yield, but reduces flower quality if upper leaves are affected. At the same time, the appearance of H. valtellinensis indicates very high humidity in the planting's microclimate, and if such conditions persist for a long time, more dangerous diseases, such as Fusarium oxysporum, appear on carnations.

In some cases, this fungus attacks flowers, causing rot starting at the tips of the petals. Under very high humidity, a dense coating of mycelium develops on the flowers. In controlling grey mold, reducing relative humidity is very effective, as well as spraying with fungicides, similar to protecting carnations from stem grey mold (see page 283). Anther smut (Ustilago violacea)

On modern carnation cultivars, this disease is rare, as few of them produce anthers. The smut pathogen is a systemic one. Affected plants are stunted and often form numerous lateral shoots. Instead of pollen grains, the anthers contain purple-black fungal spores; the plants appear dirty and covered in soot. Anther smut is widespread on other members of the Caryophyllaceae family, such as white campion (Melandrium

Fusarium bud rot (Fusarium poae)

Infection by this pathogen leads to the rotting of the inner parts of the flower, which become covered with white mycelium; otherwise,

| A ‚3 ‚ \ } „ | 4 ‘№ ит 98 4 де | \:. $7 ивы) | РУ о м = { 7’ “т { и, 7, \ |. 1 `- \ в 4 ы т я \ 1 Н [Х \ ” `\! 5! Fig. 12.4. Flower rot of carnations caused by Botrytis cinerea. the carnation appears healthy. The development of Fusarium flower rot is linked to the appearance of the mite Siteroptes graminis, which appears to act as a vector for the pathogen and, in addition, facilitates its entry into tissues by causing damage. White carnation cultivars are considered the most susceptible to this disease. To suppress it, all affected flowers are removed, and the mite that facilitates the pathogen's spread is controlled.

The most typical sign of powdery mildew infection is a white powdery fungal coating developing on the flower calyx (Fig. 12.5). The upper leaves of the flowering shoot often remain healthy even with severe infection of the lower leaves. Powdery mildew develops strongly in the autumn and winter months under very high relative humidity, which favors spore germination and plant infection. The spores of the powdery mildew pathogen are airborne. The pathogen is specific to carnations and closely related species and is found quite rarely.

Control. When cutting flowers, it is necessary to remove as much of the affected tissue as possible. Disease suppression is facilitated by high-volume spraying with dinocap, oxythioquinox, or chlorothalonil. When possible, spray flowers that have not yet opened, as the fungicide deposits on the petals.

\ The buds should be sprayed before opening, as the fungicide deposits on the petals.

The first symptom of infection is a slight chlorosis of the leaves, sometimes developing only on one side of the plant, and in individual cases even only on one side of the leaf blade. Gradually, the number of affected leaves increases, and the chlorosis spreads upward through the plant. Sometimes a purple-red mottling appears simultaneously, which resembles infection by *Phialophora*, although with fusarium wilt leaves become chlorotic, while with *Phialophora* they turn gray-green.

Fusarium wilt of carnation is a dangerous vascular disease that can quickly destroy plantings in a greenhouse. The pathogen affects the conducting system of the stem, causing dark brown staining of the conductive tissues, and persists in the soil for years in the form of resistant chlamydospores. To maintain the productivity of the plantings, it is important for the agronomist to identify the source of infection in time and properly carry out soil disinfection.

• Spread rate of wilt — up to 50 cm/month
• Symptom manifestation in infected cuttings — after 6–8 weeks
• Period of crop health during local sterilization — 14–16 months
• Volume of water for leaching bromide from soil — about 30 cm
• Permissible bromide concentration level in soil — up to 5 mg/kg

How infection spreads in the greenhouse

The development of Fusarium directly depends on air temperature. In spring and summer, the disease progresses rapidly, whereas in winter, due to low temperatures, symptoms do not appear, although the fungus continues to develop inside the tissues. As a result, infected plants look healthy until the onset of spring warmth and serve as hidden sources of infection.

The pathogen is usually brought into the greenhouse with cuttings or substrate on the roots of plants. A clear indicator of the source of infection is the pattern of distribution of diseased bushes on the beds:

• random (chaotic) distribution 6–8 weeks after planting indicates infected planting material;
• focal distribution indicates that the source of infection is the soil.

Inside the greenhouse, the fungus is transmitted through contact of root systems and is also carried by wind and water splashes. The main factor in the rapid spread of conidia and chlamydospores is excess moisture on the surface of the beds. At the same time, the pathogen's chlamydospores are extremely viable: they withstand chemical treatment and short-term heating to temperatures close to boiling.

Technologies for soil disinfection and localization of outbreaks

It is impossible to completely sterilize the soil in a greenhouse — by the second year of cultivation, carnation roots go into deep layers, where the infection persists. However, local disinfection of affected zones allows subsequent plantings to be kept in a healthy state for up to 14–16 months. For deep soil disinfection, a combined method is used.

1. Inject metam-sodium into the subsoil layer of the infected area using an injector.
2. Perform thermal steaming of the entire greenhouse.

The efficiency of steaming increases when growing carnations on isolated beds, in peat bags, or on mineral wool. When using bags, the peat can be cleaned repeatedly. To do this, it is raked to the center of the bed over the drainage system, and steam is supplied through clay pipes.

If fusarium wilt appears in the early phases of carnation development, it is necessary to immediately localize the outbreak. To do this, all affected bushes are removed together with a portion of the neighboring healthy plants. The cleared area of soil is treated with a sterilant (metam-sodium or dazomet) and covered tightly with polyethylene film.

The spread of the disease from planting to planting or within a planting can occur when moving plant debris and pathogen spores, in particular, with irrigation water. To avoid the spread of infection via footwear, a disinfection bath or mat is placed at the entrance to the greenhouse, and one should try to avoid contaminating footwear with soil from the beds, which happens especially often when cutting flowers. The spread of spores with irrigation water can be sharply reduced by introducing drip irrigation, which eliminates surface water runoff.

Fungicide application. In general, fungicides are not sufficiently effective against Fusarium wilt, although, according to some data, timely treatment with benzimidazoles, and more recently with prochloraz-manganese, proves successful. Plants are watered with fungicide solutions shortly after planting, and treatments are repeated regularly during the growing season.

Resistant cultivars. There are no carnation cultivars resistant to Fusarium wilt, but recently, breeders from various countries have managed to obtain very promising lines. For example, some hybrids based on the cultivar Oscar Beauty and a breeding line from California called Carrera 929, when crossed with other sources of resistance, gave rise to a group of plants from which selection for flower quality and viability was carried out. So far, these forms are resistant to only one or two strains of the pathogen, but they will obviously become of great importance, especially since their distribution on a global scale is limited.

Phialophora or Verticillium wilt (Phialophora cinerescens, syn. Verticillium cinerescens)

Phialophora wilt (phialophorosis) was the most important disease of carnation in Europe until the early 70s, but currently, it is encountered quite rarely. In terms of symptoms, it is similar to Fusarium wilt, but the affected leaves are not chlorotic; instead, they acquire a matte grey-green color and red spotting. The infestation is particularly noticeable in spring when plants reach their maximum development. Vascular tissues turn brown, but not as severely as with Fusarium infection. When some yellow, orange, and other light-colored cultivars are affected, bronzing develops on the leaves instead of purple-red spotting on a grey-green background. On plants affected in autumn, symptoms may develop over several months, after which the plant dies. In the initial stages of phialophorosis, the root system remains healthy, and a diseased plant is sometimes difficult to extract from the soil.

The soil-borne pathogen of phialophorosis survives in the form of spores or mycelium, persisting in the soil or plant debris. Numerous spores form on plants with the developed disease, which are dispersed by air or irrigation water. The pathogen enters the plant through the roots and spreads either through contact between the root systems of neighboring plants or via spores and plant debris (Fig. 12.6). Usually, phialophorosis spreads radially from centers, particularly if the soil serves as the source of infection. When the pathogen is introduced with carnation cuttings, the random distribution of diseased plants in the plantation becomes noticeable at first, but in each individual case, a center of infection appears, which increases in diameter at an average speed of 20–50 cm during summer months. It has been experimentally proven that the rate of disease spread decreases significantly if the accumulation of surface water on the bed is avoided, in particular, by replacing watering with drip irrigation.

Control. Methods of protecting carnations from phialophorosis are similar to those used against Fusarium wilt, but treatments with benzimidazoles in combating P. cinerescens are much more effective. Highly effective suppression of the disease is provided by watering plants with benomyl shortly after planting cuttings and then at regular intervals during the growing season. In some soils, benomyl undergoes microbiological degradation and loses its effectiveness.

Sources of resistance to phialophorosis have not been discovered. Bacterial wilt, or stem cracking (Pseudomonas caryophylli)

This bacteriosis is widespread in the USA but is almost not encountered in European countries. Affected plants show signs of progressive wilting, which gradually, sometimes over many months, covers the entire plant. The root system rots. On the stems of some plants, longitudinal cracks appear, extending to several lower nodes. The epidermis in the affected areas peels off, exposing a wide and deep crack in which agents of various types of mold, especially Cladosporium spp., sometimes settle. Another typical symptom of infection is the bending of the tops of young shoots.

In diseased plants and even in infected petioles, severe browning of vascular tissues can be observed. In addition, the pathogen causes root rot, which can be distinguished from other types of root rot also by the noticeable browning of the vessels. The spread of the bacterial wilt pathogen occurs via water splashes and during the care of diseased plants. The pathogen survives in the soil, albeit for a short time.

: й, р Г, _ м 7 \ | Fig. 12.7. Cracks on a carnation stem resulting from infection with bacterial wilt or stem cracking (pathogen Pseudomonas caryophylli). — Affected plants often become stunted. ь.

Control. Infected plants should be removed at the first sign of detection. For irrigation, methods that prevent water splashing are necessary. There are no effective chemical control methods for this disease. At the end of the season, plant debris is carefully removed and soil disinfection is carried out .

Slow wilt, or bacterial stunting (Erwinia chrysanthemi)

Bacterial stunting is a dangerous hidden threat to carnation plantings. Infected plants sharply slow down their growth, their leaves acquire a characteristic gray color, after which gradual wilting begins. Diseased bushes practically do not develop and stand out sharply against healthy ones. The entire cycle of the disease from the appearance of the first signs to the complete death of the plant takes from 6 to 8 months.

• Period until plant death — 6–8 months
• Difference from bacterial wilt — absence of stem cracking
• Infection reservoir — soil or substrate

When diagnosing, it is important to correctly identify the pathogen by key signs. The disease is accompanied by browning of the vascular system, but, unlike bacterial wilt, carnation stems do not crack. In Europe, this bacteriosis is currently not widespread. Control methods for bacterial stunting are similar to the measures used against bacterial wilt.

Leaf fasciation (Corynebacterium fascians)

A characteristic symptom of this disease is the overgrowth (proliferation) of leaf tissues at the base of the stem or at its nodes. The disease harms young plants most severely, significantly delaying their growth. At later stages of the growing season, the infection affects the development of the carnation only if the pathogen is widespread.