PHYSIOLOGICAL DISORDERS OF TOMATO

Important physiological disorders of tomatoes are blossom-end rot, catface, growth cracks, sunscald,yellow shoulder, chemical injury, andadventitious root.

BLOSSOM-END ROT. Blossom end rot is avery common problem on green and ripetomatoes. It begins with light tan, water-soakedlesion, which then enlarges, turn black andleathery (Figure 1). Although blossom end rotitself causes only local injury, secondaryorganisms frequently invade the lesion and causecomplete rot of the fruit. It often occurs in rapidlydeveloping fruit during periods of hot, dryweather and tends to have the greatest impact onthe earliest maturing fruit. A localized calciumdeficiency in the distal end of the fruit results inblossom-end rot because calcium is not a highlymobile element, a deficiency can occur with afluctuation in water supply, even for a short period oftime. Thus, moisture extremes promote thelikelihood of the disorder. Other conditions thatreduce calcium uptake by the plant, such as highsalts, the use of ammonium nitrogen, and highrelative humidity can intensify the problem. Rapidlygrowing plants are more subject to the disease.Blossom-end rot can be managed by properfertilization, water management, and plantingcultivars tolerant to blossom-end rot. Soil testing isrecommended to determine if there is a shortage ofcalcium. Liming with high-calcium limestone 2-4months before planting can alleviate blossom-endrot. If calcium deficiency occurs, foliar spray ofanhydrous calcium chloride may be helpful.

CATFACET. Catface tomatoes are misshapen, withenlarged scars and holes in the blossom end of the fruit (Figure 2). Cold weather at the time of__________________________________________________________________________________For further information contact Mohammad Babadoost, Extension Specialist in Fruit and Vegetable Pathology, Department of Crop Sciences, University of Illinoisat Urbana-Champaign. (Phone: 217-333-1523; email: babadoos@illinois.edu).

University of Illinois Extension provides equal opportunities in programs and employment.

DEPARTMENT OF CROP SCIENCESUNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN

report on

PLANT DISEASE

RPD No. 981

December 2014

-2-

blossom set distorts and kills certain cells that should develop into fruit, resulting in the deformities.The disorder is most often observed among first-formed fruit. Catface can be controlled by plantingcultivars not subject to this damage. Ingreenhouse, heating to avoid lowtemperatures can reduce catfacing. Thisincludes temperature control for thegrowing of transplants for field planting.

GROWTH CRACKS. Two types ofcracking occur in tomato fruit. Concentriccracking is a splitting of the epidermis incircular patterns around the stem scar.Radial cracking is a splitting that radiatestoward the blossom end from the stem scar(Figure 3). Cracks occur on tomatoes asthey near maturity, depending on thecultivar. Less susceptible cultivars do notcrack until the breaker stage; more tolerantcultivars do not crack until they are redripe; resistant cultivars rarely crack at all. Crackingis associated with rapid fruit development and widefluctuations in water availability to the plant. Fruitthat has reached the ripening stage during dryweather may show considerable cracking if the dryperiod is followed by heavy rains and hightemperatures. Growth cracking could be minimizedby planting cultivars tolerant to cracking, properwater management, practicing good nutritionalprogram to prevent overly succulent plants, andpreventing defoliation due to foliar diseases to limitfruit exposure.

SUNSCALD. Sunscald occurs on green tomatofruit exposed to the sun. The initial symptom is awhitish, shiny area that appears blistered. Thekilled, bleached tissues gradually collapse, forminga slightly sunken area that may become paleyellowish and wrinkled as the fruit ripens (Figure 4). The killed tissue is quickly invaded by secondaryorganisms and the fruit decays. Fruit most subject to sunscald are those that have been exposedsuddenly to the sun because of pruning, natural spreading of the plant caused by a heavy fruit load, orloss of foliage from diseases. The extent of the injury is more serious during periods of abnormallyhigh temperatures. Sunscald can be managed by careful pruning and harvesting, good foliar diseasecontrol, and planting cultivars with good foliage cover that does not break open and expose the fruit.

YELLOW SHOULDER. Yellow shoulder (also referred as yellow top or persistent green shoulder)affects the shoulders of tomato fruit exposed to the sun. Chlorophyll in this area is slow to break downas ripening occurs, resulting in a patch that either remains green or eventually turns yellow but not red

-3-

(Figure 5). The disease may affect the entireshoulder or only a small irregular patch. Theouter pericarp in the affected area is hard andwhite. The cause of yellow shoulder is not fullyunderstood. Apparently fruit exposed to hightemperatures during fruit maturation andripening express this disorder. Tomato varietiesvary in susceptibility to yellow shoulder, withthose having dark green shoulders being moresusceptible than uniform ripening varieties.Yellow shoulder can be managed by plantingresistant cultivars, avoiding exposure of fruit tothe sum, and picking fruit at the breaker stage(first pink color) and are allowed to ripen atroom temperature.

CHEMICAL INJURY. Major chemicaldamages to tomatoes are caused by herbicides.A common herbicide injury problem in tomatoesis caused by phenoxy herbicides such as 2,4-Dand dicamba. These are hormone-typeherbicides that are common components ofproducts used to control broadleaf weeds inlawns, pastures, and grain crops. Theseherbicides are prone to drift or move with waterto non-target sites. Symptoms of phenoxyherbicide injury appear primarily as a distortionof new growth that occurs following exposure tothe herbicide. Young leaves do not fully expand,are narrow and pointed, and tend to curldownward (Figure 6).To avoid herbicide injury,spray of the herbicide should be avoided whenwind may carry spray drift toward tomatoesor other sensitive crops. Also, herbicide-spray should be with low pressures coarse-spray nozzle, and spray should be appliedas close to the ground as possible.

ADVENTITIOUS ROOTS. Tomatoesmay form roots along the stem abovegroundwhen humidity is high. Sometimes it is inreaction to stress or disease. Some varietiesare more likely to develop adventitiousroots than others. The adventitious rootsmay be a reaction to drought-stressed. Itmight also be in reaction to a common leafdisease, early blight, which causes yellowleaves.