5. Equal amounts of azoxystrobin, boscalid and myclobutanil were applied to three different soy plants during Growth Stage 3. After 24-hours, each of the plants was sprayed with water. Base data, which of the following represents the order, from least effective to most effective, of the likelihood of preventing ASR? a. myclobutanil.azoxystrobin, boscalid b. azoxystrobin,boscalid, myclobutanil c. boscalid, azoxystrobin myclobutanil d. myclobutanil,boscalid, azoxystrobin Explain why you chose the answer that you did.

The answer is **(a) myclobutanil, azoxystrobin, boscalid**.<br /><br />Here's why: This question pertains to the effectiveness of different fungicides against Asian Soybean Rust (ASR). The key is understanding their different modes of action and how water solubility affects their efficacy after rainfall (simulated here by spraying with water).<br /><br />* **Myclobutanil:** This is a demethylation inhibitor (DMI). DMIs are systemic, meaning they are absorbed into the plant tissue. However, they are also more water-soluble than the other two options. The 24-hour period allows for some uptake, but the subsequent spraying with water likely reduces its effectiveness due to wash-off and leaching.<br /><br />* **Azoxystrobin:** This is a strobilurin (QoI). QoIs are also systemic but generally less water-soluble than DMIs. They have some preventative and curative properties. While not completely immune to wash-off, azoxystrobin is expected to retain more effectiveness after the water spray compared to myclobutanil.<br /><br />* **Boscalid:** This is a succinate dehydrogenase inhibitor (SDHI). SDHIs are known for their excellent preventative activity against ASR and have relatively low water solubility. This makes them less susceptible to wash-off and more likely to remain effective after the water spray. They are also partially systemic.<br /><br />Therefore, considering the water solubility and systemic properties, myclobutanil would be the least effective after the water spray, followed by azoxystrobin, with boscalid being the most effective.<br />