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Purple Power

Pest: Pink Rot (false powdery mildew)

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Pest: Pink Rot (false powdery mildew)



( Trichothecium roseum)







The fungus Trichothecium roseum produces a white fuzz that covers branches, leaves, and flowering tops of hemp. These symptoms have been confused for true powdery mildew, caused by Sphaerotheca macularis. Pink Rot is also known as false powdery mildew. It can also be confused with gray mold and downy mildew.


Plants of Afghanica heritage are particularly susceptible to pink rot.




Special Species Notes


A fungus in the division Ascomycota first reported in 1809. It is characterized by its flat and granular colonies which are initially white and develop to be light pink in color. It is found in various countries worldwide and can grow in a variety of habitats ranging from leaf litter to fruit crops.


Known habitats of T. roseum include uncultivated soils, forest nurseries, forest soils under beech trees, teak, cultivated soils with legumes, citrus plantations, heathland, dunes, salt-marshes, garden compost, termite nests, paper mill slime, and sewage sludge. It can colonize dead plant material, insect excreta, or pollen lying on the surface of leaves.


There are approximately two hundred twenty-two different plant hosts of T. roseum found worldwide. Trichothecium roseum causes pink rot on various fruits and vegetables. Levels of T. roseum in foods other than fruits are generally low.


Commonly, this fungus can be isolated from the tree leaf litter of various trees including birch, pine, fir, cotton, and palm. It has also been isolated from several food sources such as barley, wheat, oats, maize, apples, grapes, beans, hazelnuts, pecans, pistachios, muskmelons, watermelons, peanuts, coffee,  pear, banana, peaches, celery, hops, hemp, cabbage, common bean, citrus, coriander, squash, soybean, tomato, lettuce, cucumber, and  potato (Tubers get infected only from infested soil.)





The genus Trichothecium is characterized by its pinkish colored colonies. Trichothecium roseum is distinctive from other species of the genus Trichothecium in its characteristic zigzag patterned chained conidia. 2mm long, 4-5um wide


Trichothecium roseum colonies are flat, granular, and powdery in appearance. The color of the colonies appears to be white initially and develop into a light pink to peach color.


Trichothecium roseum can act as both a secondary and opportunistic pathogen by causing pink rot on various fruits and vegetables and thus has an economical impact on the farming industry.  It  produces a wide variety of secondary metabolites including mycotoxins, such as roseotoxins and trichothecenes, which can infect and spoil a variety of fruit crops.



Common Species:



Secondary metabolites of T. roseum, specifically Trichothecinol A, are being investigated as potential anti-metastatic drugs. Several agents including harpin, silicon oxide, and sodium silicate are potential inhibitors of T. roseum growth on fruit crops.



First signs:


It is considered both a secondary and opportunistic pathogen since it tends to enter the fruit/vegetable host through lesions that were caused by a primary pathogen. It grows and sporulates best in humid conditions. It can produce a toxic metabolites called trichothecenes.


Disease caused by this fungus is characterized by the development of white powdery mold that eventually turns pink. It usually affects stems/trunk, petioles, flowering tops, and dead and live leaves. Trichothecium roseum causes numerous pink to salmon lesions, which initially appear white on the surface of the plant. It has been reported that it reduces the germination potential of seeds. The pink tint starts when conidia are produced.


The fungus Trichothecium roseum has similar symptoms of  Sphaerotheca macularis (powdery white mildew) during certain phases of its development it can take on a pink hue. However, in another of its stages, it has the same white or grayish color as S. macularis, and is therefore easily mistaken for it. S. macularis develops on the surface (it does not penetrate deeper layers of the leaf) whereas Pink rot (Trichothecium roseum) usually occur on the upper side of the leaf, and on the stems.  Another way of identifying it is by rubbing your finger across the leaf: the powder leaves a mark on your finger. That might fool you into thinking that it is easy to eradicate with fungicides. Another difference with S. macularis is that this fungus is usually limited to the leaves, whereas pink rot can colonize even the stems.


S. macularis is an obligate biotrophic fungi (needs a living host) whereas pink rot is a saprophyte (it also develops on dead matter) which means that there is always a reservoir of this fungus nearby.


As a result, the fungus begins to develop on the plants helped by sticky remains of pests such as white fly, plant lice, wood lice, etc., or on remains of dust or pollen that may have been deposited on the leaves. Once it has developed and built up its strength on these remains it is in a better position to infect the living tissue. There are practically no references on the damage caused by this fungus or on its biology as a pathogen.




Life cycle


Trichothecium roseum overwinters on crop debris or in the soil.


Trichothecium roseum reproduces asexually by the formation of conidia with no known sexual stage. Trichothecium roseum is relatively fast-growing as it can form colonies reaching 9 cm (4 in) in diameter in ten days at 20 °C (68 °F) on malt extract agar. This fungus grows optimally at 25 °C (77 °F) with a minimum and maximum growing temperature of 15 °C (59 °F) and 35 °C (95 °F) respectively.


 Trichothecium roseum can tolerate a wide pH range but grows optimally at a pH of 6.0. Sporulation occurs rapidly at pH 4.0-6.5 and a combination of low temperature (15 °C (59 °F)) and high glucose concentration can increase the size of conidia.


Treatment of T. roseum with colchicine increases the number of nuclei in conidia, growth rate, and biosynthetic activities.


There are a variety of sugars that T. roseum can utilize including D-fructose, sucrose, maltose, lactose, raffinose, D-galactose, D-glucose, arabinose, and D-mannitol. Good growth also occurs in the presence of various amino acids including L-methionine, L-isoleucine, L-tryptophan, L-alanine, L-norvaline, and L-norleucine.





What to do for preventative use


Average daily temperature:

Temperatures of over 15°C / 59°F favor the development of the fungus and the spread of the conidia. In general, production of conidia is reduced at temperatures below 15-20°C / 59-68°F or above 26°C / 79°F. According to studies conducted on hops, exposure of around two hours to temperatures over 32°C / 90°F reduces the incidence of the disease.


Relative humidity:

The optimum range for germination of the conidia is between 75% and 98% humidity. At relatively low humidity rates, the fungus reacts by releasing a greater number of spores. This dispersion is also favored by sudden fluctuations in humidity. The more the ambient humidity falls and the more abruptly, the greater the number of spores released into the air. Although the environmental humidity is low, due to plant transpiration the leaf surface may be quite damp, facilitating germination of the conidia. In such cases, a digital temperature and humidity gauge with maximums and minimums is a must, since it will give you a precise idea of when these high-risk conditions arise.



The rain washes away any spores floating in the air and the likelihood of infection on a rainy day is therefore low. A layer of water on the leaves can also prevent the spores from germinating and the conidia from developing and spreading. The conidia need light to ripen, so the spores are scattered by day. The most critical time of day tends to come between 5 pm and 9 pm. Studies with hops show that spores that germinate in this time range are more likely to cause greater harm.


Soil that is wet, poorly drained or compacted. Make sure the soil drains freely before planting palms. To test the soil drainage, dig a hole about a foot deep and fill it with water. Let the water drain completely and then immediately fill it again.

Crop rotation. Rotating of unrelated crops each year will decrease the populations of many types of disease-causing organisms in the soil. Because pathogens tend to attack several members of one plant family but not another, crop rotations should involve different families. Grass crops or corn almost always make a good rotation crop. At least two years should be allowed between plantings of the sam e fam ily, but the longer the rotation, the less likely that an early-season outbreak of a disease will occur. The vast majority of plant diseases are lessened even by one year out of a crop. Crop rotation will reduce, but not eliminate, soil inhabitants that are long-lived, such as Phytophthora and Fusarium


Destroy the overwintering habitat of the pathogen, such as crop debris left in the field. The most practical way to do this is to disk it into the soil. Most pathogens are unable to survive once the crop residue decomposes, and disking it in enhances the decomposition process. Eliminate cull piles by burying before the next crop is planted.


remove dead leaves from each potted plant (while avoided stem injury) followed by application of a general contact fungicide (maneb or mancozeb) or systemic fungicide (such as thiophanate methyl)


Minimize plant wounding



No biocontrol is known of T. roseum. It's used as a biocontrol against Sclerotinia sclerotiorum in soil.


Increased plant spacing


Promote air movement and decreased relative humidity


Irrigate/water in morning or when lights are on and grow room temperature are normal to avoid prolonged periods of foliar wetness


grow crops under cover where needed to avoid excessive rainfall





No fungicides are effective. Fungicide treatments containing Dithane, thiophanate methyl and mancozeb might help. Apply fungicides after removing diseased leaves.






The link below will take you to "An Intro to beneficial bugs and beneficial insect food" it has a list (been worked on) to pests and beneficial insects






Note: If anyone has the misfortune of their plants getting Pink Rot, Please take pictures, so we can add them to this thread.




Classy, sassy, and a bit of a smart assy

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