In this guide we gather and organize key information from official notices and technical documents so that you can detect major problems in time, from insect vectors of viruses to leaf and soil fungi, without forgetting bacteria, nematodes and physiological disorders. The idea is to help you set up a practical integrated management system. and know ecological remedies, applicable outdoors and in greenhouses, and with special attention to treatment thresholds, prevention and good practices.
Whitefly and associated viruses (ToLCNDV and others)
Two species are at the forefront of problems in cucurbits: Trialeurodes vaporariorum y Bemisia tabaci. In addition to weakening the plants by sucking sap and cover them with molasses (which then becomes colonized with sooty mold), their greatest danger is acting as vectors of viruses, with the Tomato leaf curl New Delhi virus (ToLCNDV) as a protagonist in many producing areas.
In the field it is common to see leaves with many white "flies" perched on the underside, diffuse chlorosis and loss of vigor. Sticky molasses attracts sooty mold and depreciates the fruitwhile viral infections can cause dwarfism, yellowing of veins and deformities that ruin production.
The cycle is linked throughout the season: they spend the winter in spontaneous vegetation and, with the heat, link generations until autumn; in greenhouses they can add several generations throughout the year, with peaks in spring and autumn. When more than 1 adult per plant is detected in a large samplingIt is advisable to intervene with a specific authorized professional, preferably in the early morning or at dusk.
To reduce ToLCNDV, cultural measures are crucial: prevent the vector from colonizing new plantations (nets, exclusion, synchronizing transplants), quickly eliminate the inoculum (uproot and bag plants with symptoms) and avoid overlapping crops, keeping the plots and margins free of host plants.
Thrips: Damage, Monitoring and Management
species like Frankliniella occidentalis, Tabaci Thrips, F. schultzei o T. angusticeps They frequently attack cucurbits. They feed by scraping and sucking tissues, leaving punctures and silvering on the leaves, distortions and, with high pressures, scars on fruits that reduce their marketability.
A simple way to confirm them is to shake leaves or flowers over a white piece of cardboard; you will see those long, tiny insects move. Populations tend to skyrocket in the heatAlthough some species move better in spring; their aerial dispersal makes it easier for generations to overlap and "jump" between hosts.
Monitoring with chromatic traps (yellow or white at mid-height, and pink in the upper area in some programs) helps to anticipate. In seedlings and young vegetation, it is advisable to act upon observing the first mobile forms.And in adult plants, various sources place thresholds of 10 thrips per flower to decide.
As a management tool, alternate between predators such as mites of the genus Amblyseius (for example, A. swirskii) colonize buds and flowers if food is available; Avoid spraying that destroys auxiliary plants and plan preventive treatments with compatible products according to labels and current registration.
Red spider (Tetranychus urticae)
This polyphagous mite quickly colonizes tender leaves and spreads by wind and fine threads. The initial symptom is very fine chlorotic pitting. which evolve to yellowish or reddish; as the attack progresses, webbing appears on the underside and, if it progresses, defoliation and death of leaves.
It overwinters as a female in vegetation on field edges and stubble fields, and with dry and warm springs and summers it produces generations every 2–3 weeks; in greenhouses the cycle is uninterrupted. The weekly inspection is mandatory. And, if it appears, it is advisable to intervene quickly with authorized tools and compatible with auxiliary equipment.
Among cultural practices, limiting refuge vegetation on edges after problematic seasons, adjust irrigation to avoid water stress and promoting functional biodiversity can make a difference by delaying population explosions.
Common aphids and viruses
species like Aphis gossypii y Myzus persicae They form colonies on the underside of leaves, shoots, and flowers. They suck sap, deform leaves, and excrete honeydew. which promotes sooty mold and attracts ants. Beyond the direct damage, they are notable for transmitting viruses relevant to cucurbits.
Viruses linked to aphids include Cucumber mosaic virus (CMV), Zucchini yellow mosaic virus (ZYMV), Cucurbit aphid-borne yellow virus (CABYV) and Watermelon mosaic virus (WMV). If there are 5–10 aphids per leaf in a sample of 20–50 leavesVarious sources recommend intervention, always prioritizing strategies that preserve natural enemies.
Keeping margins and plots free of host weeds, pruning to aerate, and preparing the soil well reduces outbreaks. Vigilance in old leaves and flowers on zucchini It's useful, because many colonies settle there at the beginning.
leaf miner (Liriomyza sativae y L. trifolii)
The adults are small flies with yellow and black markings; The larvae excavate winding tunnels between the two epidermal layers, with S-shaped lines that may widen at the end. In severe attacks, photosynthesis is reduced, plants are defoliated, and fruits are exposed to sunburn.
Eggs and galleries can be seen when held up to the light; brown “seed” type pupae betray the end of the cycle. It intensifies in tropical climates and in greenhousesControl with yellow sticky traps and by monitoring new leaves, avoiding non-selective treatments that destroy parasitoids such as Diglyphus spp. either Solentus intermedius.
Caterpillars and other relevant pests
Noctuid moths and other caterpillars frequently appear in cucurbits, such as spodoptera, Chrysodeixis, Heliothis y Ostriniacapable of damaging leaves, stems and fruit. Symptoms range from bites, burrows, and holes in the leaves including perforations in fruit that facilitate secondary rot.
In addition, it is important not to lose sight of whiteflies, mites in general, and the occasional presence of leaf miners, because Overlapping pests are common and it forces us to prioritize interventions that do not decimate the beneficial fauna.
Foliar and soil fungi: from powdery mildew to “damping off”
Powdery mildew: powdery spots and defoliation
The most frequently cited species in cucurbits are Golovinomyces cichoracearum (without. Erysiphe cichoracearum) and Podosphaera xanthii (without. Sphaerotheca fuliginea), With tauric leveillula. They cause whitish, floury-looking stains on limbo; with Erysiphe/Golovinomyces predominate in the beam, while with Leveillula They stand out because of their underside.
Development occurs without free water on the leaf, with relative humidity varying according to species (around 65–70% for some and above 90% for others). The progression ends in dehydration and premature leaf dropwith a significant reduction in fruit quality. In seasons with a history of this problem, systematic protection is advisable when the weather is favorable.
Downy mildew (Pseudoperonospora cubensis)
On mature leaves, translucent, oily, polygonal spots appear, delimited by veins; on the underside, a grayish-purple powderiness is observed. The lesions become parchment-likeThey spread and can kill the leaf; the fruit usually comes out smaller and with worse organoleptic quality.
This pathogen survives in crop debris and thrives under mild temperatures (17–24 ºC) and prolonged leaf wetness (>4 hours). The risk is greater in greenhouses.Therefore, vegetation must be protected at the first signs of disease, and ventilation and irrigation must be managed. prevent fungus.
Gray mold (Botrytis cinerea)
It attacks flowers, tender tissues and fruits, covering them with a typical gray fuzz. It spreads very quickly in humid conditionscausing massive losses. It is essential to protect from rain and excess moisture, adjust watering and fertilization to avoid promoting overly tender tissues, and consider a homemade fungicide with milk.
Anthracnose and cucumber scab
Colletotrichum orbiculare (without. Gloeosporium) causes anthracnose with sunken, often dark, spots on leaves and fruit, while Cladosporium cucumerinum It produces the so-called "cucumber scab" with lesions on the leaf and fruit that devalue the product. Early detection and crop hygiene help to contain its advance; see treatment and prevention of anthracnose.
Gummy stem canker (Didymella bryoniae)
It causes cankers on stems that exude gum and necrosis in fruits (known as "black rot" in some contexts). In humid environments, the spread is rapid.Removing diseased tissue and preventing wounds is essential, along with rotations and moisture management.
Other less frequent foliar
Monographella cucumerina It can cause plectosporiosis with leaf lesions; although less common, it is advisable watch for unusual stains and confirm the diagnosis before treating.
Soil and crown pathogens
Phytophthora capsici It causes dampness and root and crown rot, as well as lesions on leaves and fruit. With waterlogged or poorly drained soils, the risk increasesDrainage sanitation and prevention are the first line of defense.
Pythium aphanidermatum It triggers damping off, with early wilting, especially with temperatures close to 30°C and high humidity. Zoospores are transported by soil water and infect roots; preventative treatments and disinfection of substrates and trays are crucial.
Sclerotinia sclerotiorum It produces cottony white molds and dark sclerotia; ventilation and reduction of free humidity They reduce the risk. Rhizoctonia solani (Thanatephorus cucumeris) causes lesions in the neck and young roots, with growth cessation.
Fusarium solani F. sp. (specialized in cucurbits) causes root rot; long rotations and healthy material They help to prevent. Monosporascus cannonballus y Phomopsis sclerotioides They are linked to root collapse and decline, especially in soils with a history of soil loss.
Vascular
Verticillium dahliae It causes localized wilting and vascular discoloration, with plants languishing unevenly. Avoid rotations with sensitive hosts And working with farms with no history greatly reduces problems.
Fruit rot
Choanephora cucurbitarum It initiates soft rots in flowers and young fruit; Rhizopus stolonifer y Fusarium spp. are also involved in post-harvest or field rots. Ventilation, careful harvesting, and wound management They are key to reducing these losses.
Bacteria and nematodes
The bacteria Pectobacterium carotovorum subsp. carotovorum It causes soft rots of tissues with a characteristic odor; Avoid mechanical damage, excess moisture, and contaminated tools It is essential to stop it.
The root-knot nematodes (Meloidogyne spp.) form nodules on roots, with plants losing vigor and yield. Crop rotation, solarization, and healthy plant material They are the basis of management, especially on farms with a history of problems; also consider nematode repellents.
Most common viruses in cucurbits
In addition to the aforementioned ToLCNDV, the following appear Beet pseudo-yellows virus (BPYV), Cucumber mosaic virus (CMV), Cucurbit aphid-borne yellow virus (CABYV), Papaya ringspot virus (PRSV), Watermelon mosaic virus (WMV) and Zucchini yellow mosaic virus (ZYMV). Vector pressure (whitefly, aphids, thrips) and the presence of host weeds explains a large part of the outbreaks.
Zucchini is also mentioned Cucumber Yellow Vein Virus (CYYV) and the Cucurbit Yellowing and Dwarf Virus (CYSDV)related to whitefly. Early suppression of outbreaks, avoiding overlapping crops, and cleaning margins are crucial. In zucchini Specific measures are described in technical programs.
Common non-parasitic problems
It is important to separate infectious diseases from physiological disorders and abiotic damage. Hail, sunstroke and heat stress They produce symptoms that can be confused with pathogens if the pattern is not observed carefully.
Genetic abnormalities (chimeras), "silvering" of the pumpkin, stem fasciation, sooty mold (black mold on molasses), fruit drop, yellowing and physiological spots, apical necrosis and phytotoxicities are also described. Fine-tuned management of irrigation and nutritionThis, along with the prudent use of pesticides, minimizes these problems.
Monitoring and prevention: pillars of integrated management
Regular monitoring is the best insurance. Establish sampling zones, tap leaves and flowers on white surfaces for thrips, check undersides of leaves for whiteflies and aphids, and Use chromatic traps for early detection of winged creatures. In the minecart, examine galleries against the light and place yellow traps.
It highlights several useful action thresholds: for whitefly, intervene when there is more than 1 adult per plant In a large-scale sampling; for thrips, treat upon detecting the first mobile forms on young vegetation and consider 10 thrips per flower on adult plants as a reference; for aphids, thresholds of 5–10 individuals per leaf in a sample of 20–50 leaves. Adjust these figures to your local situation.
In prevention, prioritize breaking the cycle: do not overlap crops, keep soils and margins free of host weeds, Remove plants with viral symptoms by bagging themIt programs ventilation and irrigation to reduce wet periods and avoids excess nitrogen that softens tissues.
For biological protection, rely on auxiliary agents: predatory mites (Amblyseius spp.) for thripsParasitoids of leafminers and generalist beneficial fauna. Before applying, ensure that the products are compatible and respect deadlines and labels to preserve the beneficial insects.
Chemical and biological treatments: references and precautions
In Spain, authorized products and their updated uses can be found in the MAPA Plant Protection Products Registry. The information is for guidance only and may change.Always check the label and current registration, and follow official recommendations.
For thrips in preventative programs, options such as spinosad, lambda-cyhalothrin, methomyl or spinetoram are cited, with indicative doses per liter in some sources. always subject to local regulations and labeling.Against whitefly, applying imidacloprid or thiamethoxam to the soil at planting can help, and silver plastic mulch has proven useful in reducing colonization in melon.
There are commercial references for different targets: insecticides/acaricides and bio-rational formulations such as oils/potashes, extracts, or microorganisms; for example, ecological repellents and fungicides They usually include valid alternatives. For informational purposes (according to catalogs and technical communications), examples include Mospilan®/Mospilan® Max and Teppeki® against aphids; for whiteflies, formulations such as Botanigard® 22 WP, Botanigard® 22WP, Breaker® Max, Majestik®, or Neudosan®; for mites, alternatives such as Shirudo® and biorational options like Majestik®/Neudosan®; for caterpillars, the biorational Delfin®, Turex®, and Turex® 50 WG; for gray mold, powdery mildew and soil pathogensReferences such as Amylo-X® WG, Armicarb®, or Valcure® appear in technical programs. Always verify crops, pests, dosage, MRLs, and conditions of use on the label and registration.
To protect beneficial fauna and reduce resistance, alternate modes of action and respect recommended application times: at dawn or dusk in whiteflyand avoiding unnecessary spraying. In areas with regional plant health warnings, adjust risk dates to your local phenology.
It is clear that the health of cucurbits requires a combination of scrutiny, calendar, and judgment: detect early, prevent better, and treat only when necessary. with registered products, combining biological and chemical control, and relying on rotations, hygiene and well-tuned irrigation/nutrition so that the crop reaches harvest with strength and quality.
