Diseases caused by the potyviruses Zucchini Yellow Mosaic Virus (ZYMV), Papaya Ring Spot Virus - Watermelon strain (PRSV-W), and Watermelon Mosaic Virus - 2 (WMV-2) can present similarly, making field diagnosis challenging. However, there are some distinctive symptoms that can aid in identification.

Symptoms:

1. Inward Curling: One of the characteristic symptoms is the inward curling of leaves, often accompanied by serrated leaf margins. This curling can affect only a few plants and may appear scattered throughout the field.
2. Blisters: Unique to these potyviruses are blisters on the leaf surfaces, which appear darker than the rest of the leaf lamina. This blistering is a distinguishing feature of the disease.
3. General Wrinkling: The leaves may show general wrinkling over the entire surface. Additionally, most of the leaf may lose chlorophyll, while areas with blisters retain a greener appearance.
4. Discoloration Patterns: There is a unique discoloration pattern where yellowish sections appear between green regions on the leaves. This pattern, along with the initial serrated appearance of leaf margins, can help in distinguishing these potyvirus diseases.

While field identification can be challenging due to the similarity of symptoms, recognizing these specific characteristics can aid in accurate diagnosis and management of the diseases caused by ZYMV, PRSV-W, and WMV-2.