Potato late blight: symptoms, cycle, and sustainable solutions to protect crops

Potato late blight, caused by Phytophthora infestans, a pathogenic oomycete, remains one of the most feared diseases for growers. Its explosive nature, rapid spread, and the economic losses it can cause make it a major concern for crop protection. During wet periods, just a few days can be enough to see a healthy field heavily damaged.

Understanding the late blight of potato symptoms, anticipating high-risk periods, and implementing suitable solutions have become essential to secure yields, especially in the context of a transition towards more sustainable practices.

Recognizing late blight symptoms on potato plants

Symptoms on foliage

The disease first appears on the leaves. Early signs show up as irregular, pale green to dark brown spots, giving the tissue a wet appearance. These lesions spread quickly when humidity is high.

Under favorable conditions, a characteristic white fuzz can be observed on the underside of leaves; this corresponds to the pathogen’s sporulation. As the infection progresses, leaves turn brown, dry out, and collapse, greatly reducing the plant’s photosynthetic capacity. This rapid deterioration directly affects tuber development.

Symptoms on stems

Stems can also be affected. Elongated dark brown to black lesions appear and may lead to tissue collapse. When stems are infected, internal circulation is disrupted, accelerating the destruction of the plant.

Symptoms on tubers

Below ground, tubers are not spared. Late blight can cause brown or purplish areas on the surface. When cut open, the flesh shows a granular reddish-brown discoloration.

The danger is even greater because some tubers may appear healthy at harvest but develop rot during storage, causing significant economic losses.

A biological cycle favored by humidity

Potato late blight thrives when moderate temperatures combine with high humidity. The pathogen can survive in infected tubers or crop residues, forming a source of inoculum — that is, all pathogen forms capable of initiating a new infection in the following season.

In spring, when temperatures exceed around 10°C and humidity is sufficient, spores germinate and infect young tissue. Secondary spread is particularly rapid during repeated rainfall or excessive irrigation. In these circumstances, a complete infection cycle can occur in just a few days, explaining the fulminant nature of late blight epidemics.

The control of blight on potato plants therefore relies heavily on anticipating climatic conditions favorable to its development, as is also the case for downy mildew in grapevines.

Prevention and control of late blight in potatoes

For potato late blight, anticipation is a key lever. Among preventive solutions, the use of certified seed tubers, produced under strict sanitary control, helps limit the introduction of diseases at planting and reduces initial pressure in the field. These certified tubers prevent planting material that is already infected with the pathogen.

Other preventive measures include rigorous management of crop residues, careful irrigation, appropriate rotation, and destruction of volunteer plants, all of which help limit sources of inoculum.

However, during particularly wet springs and summers, these agronomic measures may be insufficient. An effective strategy must allow interventions both early, to secure the crop, and during the growing season, to slow or stop disease development, particularly at key stages such as pre- and post-flowering.

Towards more sustainable protection against late blight

Protection programs still rely heavily on contact and systemic fungicides. However, their use is increasingly regulated, and reducing chemical inputs has become a priority in all sectors.

In this context, growers are looking for solutions that maintain high efficacy while respecting environmental sustainability. The goal is no longer just to treat, but to integrate multiple levers into a coherent integrated protection strategy.

OPSeed75: an innovative solution for potato late blight

It is within this framework that OPSeed75 fits. It is a grape seed extract (Vitis vinifera L.) concentrated to a minimum of 75% polyphenols, recognized as a basic substance* by the European Union. It is characterized by the presence of procyanidin oligomers (OPCs), phenolic compounds capable of exerting a direct action on the pathogen responsible for downy mildew.

When integrated into a global strategy, OPSeed75 supports growers in reducing chemical inputs without compromising performance. It fully aligns with integrated protection approaches, where prevention, monitoring, and sustainable solutions combine to secure yields.

Facing a pathogen always capable of surprises, adopting a proactive and innovative strategy is now an critical factor for sustainably protecting potato crops.

*Conformément à l’article 23 du règlement (CE) n° 1107/2009, une substance de base n’a pas pour destination principale d’être utilisée à des fins phytosanitaires, mais est néanmoins utile pour la protection des végétaux ; n’a ni d’effets nocifs immédiats ou différés sur la santé humaine et animale, ni d’effets inacceptables sur l’environnement ;et n’est pas commercialisée en tant que produit phytopharmaceutique.