They have been successful against mycosphaerella outbreaks.是什么意思？

They have been successful against mycosphaerella outbreaks.

它们可有效地防止球腔菌的大发生.

they

pron. 他/她/它们，人们，大家，政府，当局，她们；

例句
The storms had abated by the time they rounded Cape Horn.
他们绕过合恩角时，暴风雨已经减弱。

have

aux. 用以构成完成式及完成式的不定式，表示已经…；vt. 有，具有，拿，取得，从事，必须，不得不；n. 〈口〉有产者，有钱人，富国，〈英俚〉欺骗，诈骗；

例句
He did have a real knowledge of the country...
他对该国的确知之甚多。

been

v. 用来表示某人或某物即主语本身，用来表示某人或某物属于某一群体或有某种性质（ be的过去分词 ），在，存在，不受干扰，去过了，be的过去分词；

例句
Have you been able to have any kind of contact?...
你联系上了吗？

successful

adj. 成功的，如愿以偿的；

例句
...a successful advertising agency.
一家成功的广告代理公司

against

prep. 反对，对…不利，紧靠，以防；

例句
His hand brushed against hers; it could have been either accidental or deliberate.
就在有意无意间，他的手轻轻拂过她的手。

outbreaks

n. 爆发，突然发生( outbreak的名词复数 )；

例句
The recent outbreaks of cholera are a timely reminder that this disease is still a serious health hazard...
最近霍乱的爆发及时提醒了人们该疾病仍然会严重危害健康。